I'd like to think that the Strawhats have experienced the hardest challenges and have grown more than the other rookies, but that's really a pet theory.
The fact of the matter is, Kizaru, Kuma, and maybe even Garp are going to be the final walls for many of the pirates going into the new world. The Strawhats got a lucky break with Rayleigh behind their back but for almost everyone else, it's pretty much the end of the line.
Kuma, first of all, is bent on kicking some super-rookie ass. He's even taking off the gloves for his fight. Law and Kidd's chances are slim. They'll be lucky to make it through to the new world.
Kizaru's here already, with a flash intro. He's most likely here for the Strawhats, but he's also going to clean up along the way.
Garp is coming to deal with Rayleigh, so I don't think Rayleigh is going to stay with the Strawhats for long. He'll coat and be on his way, or so he'll intend to. I'm not sure what the confrontation of Garp and Rayleigh is going to be.
The Strawhats have overcome some insane odds. Crocodile, Eneru, CP9, they're some of the Grand Line's toughest challenges. It sounds like Kizaru will be another one. But let's look at the other rookies.
Bege is wuss, the moment he knows about Charlos getting punched, he's panicking and running away.
Bonny is running away with contempt for Luffy and Zoro. She'd rather avoid trouble as well.
Although Apoo is looking forward to seeing the admiral, the rest of his crew are pansies. Not looking good for him either.
Urouge, although seems to have guts, I don't think he's nearly strong enough to handle the threats on the isles.
Hawkins is still a mystery, but if his predictions are right again, he'll pull through.
X Drake, I want to see more of him. I hope he survives his encounters and maybe we'll see him again at Merman Island. However, although we see 2 of his weapons, a sword and a mace, I don't know what else he's got.
Kidd and Law are currently tag teaming Kuma, and from what we've seen before, Kuma's way stronger than what his former bounty says. An invincible body, weapons could be all over, teleportation, and a super Devil Fruit ability, all Kidd and Law can hope for is running away. And don't give me that "Kidd's got magnetic powers so he owns Kuma cuz Kuma's metal" crap. It he could he'd have done it already.