Well, it depends on what you expect out of your angel.
If you want the marker to be able to be adjusted to all the latest tournament rules, then the A1 would probably be your best bet out of the box. The a4 board doesn't have the ajustability/modes that the A1 boards do.
The A1 is smaller and lighter, and honestly shoots smoother than the A4 series markers. The A1 is very effiecent as well. It only comes with a 45 frame though, so if you like 90 frames you are out of luck on the A1. I like the overall package of the A1 being small, light, fast, effiecent, and the fact that the board does everything you could possibly want and more. Parts aren't hard to find for these unless you are looking for a ram. The last shipment of rams hasn't hit the US yet.
A4 series markers are extremely well built and fast markers. A4's are probably some of the most reliable markers WDP ever built. They are solid, rugged, and shoot great. Parts are starting to become hard to find for these, and eyes tend to be in short supply. They come with a 90 frame, but you can put a 45 frame on them if you want. Its nice to have a choice.
I shoot A1 platform angels. If I didn't, I would honestly be shooting A4 platform. You can't really go wrong with either, it just depends on what features are important to you.
TEAM METHOD - D.O.G.'s Boy's
Custom A1 fly collector (Looking for wonderboy a1 fly)
WANTED: Blue angel A1 grips
Wanted - Angel A1/SB/AR:K parts and markers broken or working