[Autumn]

Elite engine is far better for people who are doing the classic conversion kit stuff, so most people. The others can be good for oneshot build/when you are rarely using basic attacks.

Kiss farewell is unique because it can become a bow

Elite Engine is probably about the same performance as The Kiss Farewell's potential when it procs, the problem with Kiss Farewell is you need to kill something, but hey if there's ever a wraithguard on the field thats pretty easy in pvp. The unique thing with TKF is that it stacks with Conversion Gloves + Shock Collar for the ability to generate 2 charges per turn, a higher risk but higher reward option than elite engine.

TKF is not unique because it can become a bow, mutation is unique in that it can create an excel bow, and there is a difference in that statement. TKF is unique due to it's handgun status, increased critical damage and the aforementioned potential.