Pianist_1210, there is a thread on this very subject on the Diploma forum - have a look.
As Katyjay says, each board requires a very similar standard. However, as each board has a different exam structure, you may find that one suits your strengths better than the other. (This may be why your friends think it's easier - simply means it's easier for them personally, rather than easier as a whole)
Another thing (which you'll also find discussed a lot on Diplomas!) is that works appear at different "levels" between the boards (eg at LRSM for AB and maybe ATCL for Trinity). Don't be fooled - there are works on the AB Diploma syllabus that appear in the AB Grade exams! You need to be playing them at a much higher standard to pass the Diploma, and the same piece would need to ramp up in standard between the levels on the same board's exams.
All the best, and for heaven's sake, don't rush into the exam. It's a big leap from Grade 8.