AEA Maths Entry Deadline?Watch
However, Warwick requires a Distinction in AEA or a 2 in STEP, I believe according to TSR maths records no one who has got a distinction in AEA has got less than a 1 in STEP due to the obscenely high grade boundaries for a distinciton (≈80% compared to ≈45% for 2 in STEP) so I leave it for you to find out which better suites you. STEP is mainly testing your ability to tackle long questions and your ability to select the correct questions with little to no aid whilst AEA is much more about how rigorously you know you single maths specification. If you know the A level syllabus back to front and could answer every question in it you will likely fair very well in AEA however you do not get a choice in questions. This means unlike in STEP if a topic comes up that you are weak in (vectors and binomial notation for me) and is worth a large chunk of marks you may be in trouble. You have 3 hours for both exams though (3 hour 45 with 25% e.t. like me).
Hope this helps.