>>6235892You're going to get a lot of recomendations that hit certain criteria but I'll target what I know.
Part 4 has a pretty solid lineup of characters and colorways. Your hardest catch will be Kira and Killer Queen across the board (1st, 2nd, and WF) and Okuyasu. If you care about articulation and the general fun of a figure then Star Platinum is your best choice since Medicos gave him a proper setup of butterfly joints, joints in the shoulderpads, and waist rotation with biggest detractor being his colors and headsculpt for many people. Everything else is tied more to acessories, what character you like the most, and what colors you want.
Part 5 is a more interesting with the acessory department with some fun scene specific ones to effects like Mista's bullets and Diavolo's blood. King Crimson is my top choice however since he's fun to fiddle with even though you have to be careful around his shoulderpads since they restrict movement and can easily snap if you push the joint on it too far. Bruno and Mista is another recommended SAS due to accessory choice and display potential.
Part 6 is held back by colors for some but you have standouts like Annasui's effects, White Snake's general build quality and posability, and I guess Weather Report's cloud effects but that's minor.
You have quite a selection so I can't cover everyone in near detail but if you need shots to see what they can do then go to the review section on the OP for various posing and action shots.