AEA is much more similar to A-level Maths in style of questions. It's entirely Pure, unlike STEP which has Applied. However, all AEA questions are mandatory and the grade boundaries are harsher. Fudging the final bazillion-mark question on an AEA paper can cost you a Distinction.
Are you asking because of a Warwick 2 / Distinction offer? I'd say try an AEA paper or two, if you can get Distinctions reliably that may be worth a look, but a 2 in STEP I is definitely doable.
(Assuming you're talking about the Warwick offer
Why not prepare for both, do both, then you have two chances at getting in?
Here's an AEA Megapack - just has all past papers, markschemes and reports, plus specification and formula book. I have the grade boundaries somewhere too... edit: they're below
http://www.mediafire.com/?n2suv2828hngr8lGrade BoundariesMy strategy was to start with the Silkos booklet "AVPI Core Mathematics", do 5-10 questions from around the start, then print off one past paper for each STEP and do questions from those.
S1-2 should be OK for STEP I and II. The Stats requirements for STEP III are weird - there's bits and bobs from all modules up to S4 on OCR, but there's a lot on those modules that you really don't need!