Flashfire has 15 EXs.
The XY Base Set has 14.
Pretty much a tossup either way. I'd recommend getting a booster box from either set, the XY Trainer Kit, and one or both of the XY Elite Trainer Boxes (there's a red Yveltal and a Blue Xerneas version, but they're $40 apiece). The Trainer Kit will walk you both through how to play and the Elite Trainer Boxes come with card sleeves (Xerneas box has Xerneas sleeves, while the Yveltal box has Yveltal sleeves), damage counter die, a coin flip die, a small cardboard deck box, some status tokens, and a small amount of each Basic Energy type (and they're also sturdy enough to act as collection boxes).
That'd be a lot of money at once, though, just a heads up.