1. Any archetype that makes the Bard more martial and like the Magus, like Arcane Duellist (I just really love the Magus).
2. Vivisectionist Alchemist, I like bombs, but an alternate sneak attacker is great.
3. Preservationist Alchemist. it's a fun summon build, and I like the idea of "summoning" monsters preserved in a jar.
4. Titan Mauler Barbarian, is great for insane massive weapon shenanigans, but let's not have Halfling barbarians get all these bonuses on all medium creatures, it kinda ruins the intention behind the archetype.
5. Zen Archer Monk. I love this different take on archers and monks
It's a shame not more of the base and hybrid classes will be in the core rulebook, because they are some of my favourites. Any archetypes that function somewhat similarly to those classes will certainly be appreciated.