Obviously, ANIMAL KINGDOM is the class of the Belmont. SHACKLEFORD is certainly what we would call a "running fool" and obviously the most dangerous foe. The odds will surely reflect this.
It's figuring out which you think will come out on top, and which may run out of the money. Obviously, the speedball is most likely to fade, but one never knows. After all, both have run in both triple crown races and could be down for this.
So it boils down to who else to put in the exotic wagering. MASTER OF HOUNDS, NEHRO, and MONZON are all bred for much shorter races, but the first two of these are outrunning their bloodlines so far. Neil Howard is always a danger to run in the money, though his PRIME CUT looks a cut below. The one medium priced one that I would toss out as a "sucker" play is SANTIVA. This is because he was primed for his best effort in the Derby and didn't deliver. He has flunked two straight races, and of course if you own him, you know you have a nice animal, but he isn't a grade one stakes runner. The connections may be hoping he's one of those who runs a big fluke win every now and then, but this means a win, not "in the money." He's a toss out in the exotics, unless you have a hunch to put him on top as a fluke winner.