To give you perspective on how open ended that question is... Poorly formatted wall of text incoming!
Current competitive play sees a lot of junkers and pyramidions.
Frequent ships are mobulas and galleons.
Rarely seen are goldfish and spires.
Almost never seen are squids.
A lot of things factor into the choices for competitive ships, including ease of use (for pilot and crew), risk/reward for the gun points, current meta, and teamworking capabilities.
In no particular order (other than junker being last), my opinions...
Pyramidions are one of the easiest ships to set up with a crew, and the logic can be pretty straightforward. It will always be popular unless heavy nerfs go into effect. However, it has a lot of drawbacks in that setting up a trifecta sacrificies almost every advantage the pyramidion has in order to get one extra gun firing: not good. It can be tough to use a pyramidion effectively in long range combat, and it isn't as durable as it sometimes seems. It can work well with enemies, but is not the best ship for providing support fire at range, and tends to be controlling at shorter ranges.
The biggest drawback is that the pyramidion is mostly one-dimensional. You are going to load out for one range, and if you can't get into that desired range, you are kind of helpless.
Slightly above average power, but not OP.
Mobulas are very difficult to crew. Every crew member must be willing to take a gun, and also be aware of when to go for repairs instead of shoot. It requires a lot of balance, but has quickly found its own niche. The raw firepower available makes it an excellent weapons platform, and it can be loaded out to join its ally in a close-range set-up, or a sniper build. The big drawback is its maneuverability and seeming fragility.
It is slow to move forwards or backwards, and slow to turn. It has excellent vertical movement, but this can fall short of saving you in tight situations. It theoretically isn't as squishy as it seems, but it is very light, and so can be pushed around very easily, making it easy to push it into positions it does not want to be in. Generally mobulas are built with a single range in mind. It can outfit to fight at multiple ranges, but is most effective concentrating firepower at a single range. The best counter is to not be in that range.
Above average power, but balanced by the absurd difficulty of use.
Galleons are tough, but not particularly maneuverable. Combine this with the poor turning arcs of the heavy weapons, and you have a ship with very large blindspots and a very big hitbox. Galleons make excellent support ships, and can be excellent killers, but are mostly reactive ships. Since you have to turn away from an enemy to shoot, you lose control over the engage distance. Because of this, your gunners need to be accurate with all gun emplacements when in arc, otherwise your enemy will quickly change the engagement distance and put you at a disadvantage. If your gunners are accurate, you can demolish foes simply through brute firepower.
The high amount of health galleons have also makes it easier for them to tank while their ally comes to help. This is a team oriented ship, that needs to support and be supported. Again, your crew needs to know and understand their role. Good gunners help a lot.
Big disadvantage currently is that a lot of ships are running gun disabling builds (artemis fire destroying guns) which takes out your heavy guns before you get to fire them. This alone makes the galleon a little weaker than it used to be, but not much so.
Slightly under average power just due to the meta, but still a very good ship with teamwork.
Goldfish are almost exclusively support ships currently. One weapon alone, even a heavy weapon, is not going to be a killer. This combined with e pilot requirements to get the goldfish to use the sideguns make the fish very difficult to fly and kill quickly with. It can work well at disabling and supporting, but it is currently plagued with disabling spam. Artemis/mercury guns can easily destroy that front heavy gun: the one best the the goldfish has going for it. Once that gun is down, the goldfish is almost helpless.
That said, working in tandem with an ally, it has good durability, is pretty maneuverable, and can lay in precisely the type of damage that their ally wants to mesh with their ally's build.
Overall, underpowered at the moment, and probably in need of a little bit of thinking about what is causing this. The heavy gun is a little too susceptible to being disabled, and once it goes down, the goldfish is severely weak for the duration of the long rebuild time.
Spires suffer from the same heavy gun disabling as the goldfish, but are also as brittle as... something very brittle. Their gun emplacements allow for very high quantities of damage, with the heavy weapon in arc with multiple light guns. Spires are very high risk-high reward. Failing to kill an enemy at the right moment usually ends with you being destroyed very very quickly. You don't have the durability of other ships, so you need to either disable or kill enemy ships before they have a chance to kill you.
Working with an ally well, spires can lay in extremely good fire. Good gunners and good piloting makes spires, but since they are unforgiving it is very easy to slip up and be taken out quickly, leaving your ally vulnerable.
Probably slightly underpowered due to the current state of heavy gun disabling, but sitting in a pretty good place in the game.
Squids are... well, squids. I'm not sure where squids fall right now. Make them faster, and even good pilots won't be able to fight against them. They will be able to easily acquire blind spots and lock down opponents far too easily. Leave them as is, and noone will take them competitively because they are difficult to get in the best position, and are extremely unforgiving of slight mistakes. I really don't have an answer as to where squids stand right now. They seem to be support ships, but can also run as quick attack ships.
Junkers... The actual interest here. I listed out the other ships just to give you a feel for how I see the playing field, so you understand my view on junkers as is.
Junkers are perhaps the most versatile of ships. With 5 gun placements, it is tied with mobulas for 2nd most guns, just behind the galleon. It turns faster than the mobula or galleon, and accelerates better. It has better vertical movement than the galleon.
Additionally, your guns are not all pointing in approximately the same direction. This means that unlike the mobula, whose strength is firing all of its guns at once, the junker is perfectly suited to use ~half of its guns at once. The sides are balance, with equal potential for damage off of either side, allowing the pilot to choose guns for each side without having to favor one side, or make any particular choice between long or short range. It is blindingly easy to set up a junker to have a close and short range side, each with 2 guns in arc at once. The 5th gun on front is a bonus for your playstyle, to match your preference.
The hull is strong and very thin: hard to hit, and pretty durable when you hit it.
When under enemies, the balloon acts as a very large shield from the normal piercing attacks that are used for quick kills in the meta.
The biggest weakness is that unlike the strong forward-facing ships, the junker is best when turned at an angle, meaning you lose a little bit of control over engage distance. You have to do your best to hold an enemy at the ideal range, but you don't have full control. Additionally, your balloon, while capable of providing protection, is a large juicy target. If your balloon goes down, no ship offers a larger, easier, weaker hull hitbox. Losing your balloon in a junker is just about the worst thing possible, as you lose positioning and open yourself to significant real damage.
While the junker offers the strong versatility of having close and long range sides balanced on one ship, it has several other flaws. It tends to run a supportive role, as it can't close with the enemy like the forward facing ships. This means that it requires more deft control and teamwork to balance with your ally and make sure your fire supports one another. All the components are squished together. Burst rounds on explosive weapons will damage most components on the ship. The top speed is not as high as most other ships. The coordination needed from the crew is higher, since there are no simple layouts for who takes care of what.
Overall, I would qualify the junker as slightly above average in power, due to the versatility of use. This is not to say it is the strongest ship. Muse has done an excellent job of balancing, and every build has a counter. The junker is just better capable of handling different situations than other ships seem to be.
TL;DR: Junkers are versatile, with easy setup for short and long range sides, but the game is fairly well balanced, and while the junker is currently strong, it does not qualify as overpowered.
