IMO, the second one is slightly more useful in the short term as Legendary's are only useful for Attacking, but you won't go too wrong with either. The first one you can soak a bit more damage but do slightly less damage. The second you can do slightly more damage but you might need to dodge a Fast Move or two to make up the difference. But again, not a whole lot of difference.
Going to depend on how well you can Dodge; if you can reliably dodge, go with the 87% IV. If Dodging is an issue (for whatever reason - due to connection issues, phone issues, etc. On my old phone I can't reliably dodge due to the age of the phone and the crappy processor) then go with the 91%.
