I've only read through part 3, so I only have one series of stands to choose from. That being said, I pick Osiris. It's not that his power is my favorite, it's just that I love the scenario he put the protagonists in. I love the idea of the non-violent one nearly beating them, and the bluff used to beat him was surprisingly intricate. Jotaro didn't just act confident in his cards, he had Star Platinum bring him drinks and other such small things while D'arby wasn't looking, just to make him think that there was a chance that he might have changed his hand. To top it all off, raising the ante to force D'arby to tell them about Dio's stand if he lost was brilliant. He knew the regard that Dio was held in by his followers, and he knew that the stress of agreeing to potentially betray him would get to D'arby.
Not only that, but it made excellent use of Jotaro's personality. I didn't like Jotaro as a main character nearly as much as I'd liked Joseph (although, to be fair, it's pretty damn hard to be a more likable protagonist that Joseph), and I didn't care for his cold, emotionless demeanor, which was in contrast to the emotional sincerity and expressiveness of Jonathan and Joseph. This scenario was perfect for him. His quiet yet imposing demeanor was perfect for a poker game, and even better for the bluff.
Although the OP didn't ask for it, I'm going to list my least favorite Stand. I hate to say it, but it's Silver Chariot. I like his design, and I like Polnareff; in fact, I think he had some of my favorite fights in the series. However, it doesn't feel like Silver Chariot's abilities bring much of anything unique to the group. He's fast, and incredibly precise . . . just like Star Platinum, who also has the benefit of incredible strength. Sure, we're told that his sword can cut through just about anything, but off the top of my head, the only time I remember that really mattering is when he fought Abdul, and used his sword to slice through his flames with ease.
EDIT: I should probably specify, when I'm referring to D'arby, I mean D'arby the Gambler, not the Gamer. I know it probably became obvious as soon as I mentioned poker, but I figured I should still clarify that.
