It is a dilemma because of this:
In the current raid meta, the attack stat is by far the most important stat. Right now it is all about dishing out the most damage in the least amount of time. A high defense stat might even be a detriment here, because while you will last longer, you will gain energu slower, so in the current meta it goes attack > stamina > defense.
However, that is just the current meta. Nobody knows what the future brings. Given that, the 93% suddenly looks a lot more interesting.
Finally, in actual battles there are so many random factors. These two Moltres you have will perform almost identically. You will likely never notice any difference.
In other words: if you like the idea of your having a 93% moltres, go for that one. You'll likely never know the difference. On the other hand, if you are a hardcore raid min-maxer, then the 82% will probably do a teeny bit more damage (while lasting a teeny bit shorter) in most cases.
Whatever you do, it won't make much of a difference.
EDIT: Also bear in mind that a single extra power up or two will make the effective attack stat of the 93% as good as the 82%, so that is also an option.
