Ok, here comes the summary.
We all love Bon, we all love Croc. Well, the sensible ones among as anyways. It's a tough choice, that much is definitely true. But, let's look at this from all the perspectives we can, preferably upside down, because that's my favourite perspective.
Bon-Chan is a wonderful character. He's introduced as a friend, quickly turns out to be a threatening enemy, barely gets defeated, then returns at Impel Down to fight with Luffy together and ends up being an amazing ally, sacrificing himself. Accordingly, he's been in the finals already against Whitebeard. Tournament wise, you could say he's got Enel's spirit with him, and me being one of the greatest Enel supporters here (only after Gekko and Masterking if I dare say so) values that.
HOWEVER.
Crocodile, man, Sir Crocodile. He's the first actual big-arc villain, with a massive build up to his introduction, after Mihawk the second Shichibukai introduced and, thanks to the former's display of power dominating Zoro in their fight, is accompanied by huge hype. Which he lives up to, every great second of his appearance. Crocodile is one of the characters that, even being introduced as a grand-scale villain, is just likeable, a character that you want to see defeated nonetheless, but whatever he does, he does it with class. Luffy standing up to him for the sake of his friends is wonderful since you just know how immensely powerful he must be, he's the head of this enormous gangster mafia group where the crew already had problems fighting against Mr. 3 and Goldenweek (granted, that was a hax fight on Little Garden, but that wasn't apparent at the time) - one could only imagine how powerful the teams of Mr. 2, Mr. 1, and finally, the Boss himself had to be.
Having Robin on his side is not a bad thing either, who was introduced as soon as Whiskey Peak - man, all that build up. Crocodile is an outstanding character, a despicable, evil, slightly insane, but still likeable and awesome villain, that defeated Luffy technically 3 times and pushed him to his utmost boundaries at the time. Being the first Logia our protagonists faced is another bonus, making him seem invincible at the time, although now of course, Haki, bleh, whatever.
The thing is, despite being defeated by Luffy at the end, you never had the feeling he was "weak", and then he suddenly reappeared at Impel Down, too! Oh man, that re-introduction, saying he wants to take Whitebeard's head, who we know was the "most powerful man in the world"… Then helping Luffy and tagging along only to fulfill his own goal, but teaming up with him despite having been defeated previously, not wanting to admit he actually WANTS to help him - as we've seen when he single handedly stood in the way of Akainu, charging after Luffy, and at the same time protecting a big group of the Whitebeard pirates. Despite his relatively early introduction (and defeat), he's still a powerhouse. And you know he's going to be back, in the New World, stronger than ever.
Now, regarding who deserves the title - it's Crocodile. He could be the first villain to take the title, and after Enel's defeat last year, I think that as an Enel-supporter, my vote has to go with Crocodile now as well, since they are both fantastic villains. Bon-Chan is great, but it wouldn't feel as epic if he won. It wouldn't be "first villain" or "first non-Strawhat" or something like that. "First villain", now that's awesome.
So, all of you, think about it, think about who would be more memorable taking the title, think about the fact that no matter if Enel was defeated by Bon-Chan - as a villain, he would support Crocodile. And that's what you should do!