M4 is definitely easier to use when you're close to the ground. I'd also say it has the best controls as far as mag changes and fire select is concerned, so it's easier for most people to use overall. This is getting more subjective though.
As for upgrades, externally the M4 is probably best, but there are plenty of AK and MP5 options as well. They're just not as readily available.
Internally, the AK uses a V3 mechbox so if you REALLY want to push performance without shelling out for a mechbox machined from a solid billet, the AK is more likely to take you there. That said, the V2 isn't a slouch by any means. I'd say about 80% of airsofters here run (or at least own) an M4 or variant and many are upgraded and running fine.
Either way, and AEG is an AEG. Pick the one you like the most, and you can probably make it work just as well as anything else.
Vita, Passione e Pistole
Last edited by tunabreath; June 15th, 2009 at 19:12..
Reason: boom! comma shot!