At the 12th, you'll have a shallower angle at the bridge, but a steeper angle at the nut. The lower frets will have more of a difference between bottom string frets and top string frets than if you have the perpendicular point at the 7th fret, which can make it more difficult to play stretch-tastic riffs. Conversely, there is less of a difference at the higher frets, which could be argued to make it easier to play solo work. I don't think this would make much difference, tbh. I think the 7th fret is ideal for me because almost all of my work is done down there, and lead work isn't actually any more difficult with the fanned frets than parallel frets (if you ask me, it's easier, because the direction of the fanned frets is quite ergonomic at the high frets (and perversely also on the low frets, I haven't worked out why this is, yet, but it's cool!).
Hope that's in some way clear, Fernando... it's clear in my head but my fingers might have mis-translated it!
Roo