Master Chymist for the alchemist. It's currently a prestige but there is no reason it couldn't be an archetype. It's absolutely oozing with good flavor. Runner up is Promethean Alchemist because it's also got really awesome themes to play with. I love playing mad scientist type characters and Alchemist is one of my favorite classes.
Monk of the Empty Hand for Monk. I have a unhealthy obsession with improvised weapon builds and this archetype. Until recently it was unviable at the level magic weapons became relevant, but we eventually got Gloves of Improvised Might which solved that issue. If magic items are as essential to progression please include some way to scale improvised weapons. Runner up is Tetori for doing cool superhuman stuff like stopping freedom of movement or polymorph while grappling. Tetori could probably be handled by Legendary skill checks.
Eldritch Guardian for Fighter. Feat sharing for familiars is really cool and I love the dichotomy of caster familiars being frail and cowardly while the fighters familiar is tough. If familiar archetypes aren't making it please include mauler's size up as a class feature for Eldritch Guardian(perhaps as a archetype specific fighter feat). No runner up but I really love the Iron Caster build that is floating out there for fighter and I'd like to see something similar enabled for fighter perhaps via an archetype. Maybe give up some feature for extra resonance or something.
Kracken Caller for Druid. I'm biased in that I love playing octopus types of characters but I'm never in aquatic campaigns. This is one of the only Druid archetypes that makes it feel really distinctly different to me. Runner up would be something like the Shifter. Since the Druid does the Shifter's job so much better I'd rather see it as an archetype that gives up casting for some toughness or combat power. Spells are often an afterthought for my Druid builds, wildshape is what defines the class to me. Also like to note that I thematically adore Oozemorph shifter but it totally fails mechanically for me because I want to play as an Ooze. Oozemorph as is does everything it can to make you avoid playing as the ooze which is super lame.
Last up is Juggler Bard! I just recently discovered this archetype but it's cool as hell! Being able to carry extra objects is such a neat character concept and I really hope to see it in PF2E. Runner up is Sandman just because the selfish Bard seems like a necessary option to have available when building a Bard.