KPMG would be your option if you want to work in Tax. The way things are in the big 4, as you maybe aware, you cannot audit and provide tax services to a plc under SEC rules. So as result, PWC have the bulk of the audit work and KPMG have the tax. Them being number 1 & 2.
I just finished my AITI, in ernst and young, and I noticed at the graduation on friday last night there was a hell of a lot of people from KPMG more than any of the other big 4 firms, esp PWC.
Best of luck- you are in a very fortunate position - dont let it go to your head though, they are not the easiest practices to work in.
Secondly I would attempt your AITI part 2 before your FAE's why not sure. All the trainees in E&Y who did a masters did it that way part then FAE then part 3. I am surprised at PWC insisting otherwise
Oh yeah another point is have you any friends in either firm? - these places are so big that any friendship does help