ARES have top notch externals. Few others come close.
However, their internals are crap and proprietary. Their guts aren't Tokyo Marui compatible like everyone else. Granted, their internal designs are innovative (like quick-swap springs), but the parts are made of substandard, cheap materials. Good luck finding spare parts when they break. And it WILL break. The only question is how long until it happens.
Dealing wiht ARES customer support is an exercise in frustration at best. If you do a bit of searching, you'll find a LOT of ARES owners that now own really expensive paperweights that they never even got to a game before the internals decided to snack on themselves. ARES support is pretty much non-existent and there are no spare parts available.