Junker versus metamidion with equal level crews, the junker wins hands down as the armour will outlast that of the pyramidion, however as mentioned before it also depends on circumstance, if the enemy is packing balloon hitting power the junker has to utilise its versatility and in many cases this boils down to range.
If we are not talking high level play but pub matches, then I agree with Silverst when he says a front Artemis is not a good choice because more often than not the front engineer will become too focused on shooting and ignore orders to repair often leaving other crew to over work...
Again circumstance.
The junker is a very versatile ship and with a good crew and captain very effective, and I firmly believe any advice from a member of the duck clan should not be taken lightly as they are the masters of this ship. (I been watching old streams where I can
)
As for pyramidion trifecta, yes easy to get but it leaves you open to a ram from the enemy which will knock your front guns off arc and keep enemy in arc, very dangerous.
Mobula trifecta, yes very easily accomplished but the mobula has other weaknesses such as an even bigger target than that of the Junker.
As always circumstances.