Which Charizard Should I max?

I would go with the 87% if you really want/need to max one. Charizard is not really worth the dust if you don't have a surplus of it.

I know the 98% one may be tempting but toss that one out of consideration. Its important that you have blast burn. The difference in IVs will make such a little difference, the move will be more important.
Another consideration is do you have any good/powered up moltres and entai yet. They will still be best to invest the dust into. If you arent worried about the dust and would rather save rarecandy then you could consider maybe powering up two charizard?
I would choose either the 87% because its already lvl 33, so youll save resources and it has high atk ivs. If you really want a shiny maxed id go with the 82% if you dont mind using the extra dust/candy.
Focus on the highest atk iv while saving resources, so for me the 87% is the best choice. Its up to you though if you want the cool factor to go with it. You can always power up more in the future if you want.

When I max out mons, I usually go for the best stats/moves and don't pay attention to level, so I'd go for the 93% or one of the shinies (if you care about appearances). I can't tell if the first stat is HP or Attack.