I agree with the earlier posters – Blaster, and by a mile. Soundwave is actually one of my favorite bots, but Blaster is basically just as powerful and fires *significantly* more often. Boosted properly, he might be the most powerful bot in the game (even ahead of Dead End), and can take out Unicron without breaking a sweat.
@fumuthabeotc, Energon Grimlock is still in the upper echelon of bots (except arguably on the spark run), so I’d stick with him.
For what it’s worth, my purple crowns are Blaster, Soundwave, EG, and Dead End, with Ultimate Megatron as a gold crown (I stopped promoting when they nerfed him). I’m looking to promote another myself though (I’ve got the sparks) – I’m thinking Energon Starscream, Ratchet, or maybe Energon Lockdown. Anyone have an opinion?