The best of the best!

There are quite a lot of airsoft guns out there but they make coming to a decision a lot more interesting. $200 is more than enough for a good AEG and with $500, I'd have suggested the same gun with upgrades.
The grand old question of which AEG is best will never be solved. It's like asking which gun or car or country or state is best.
I own the JG M4, it's a good gun but will need new bushings and shims to achieve the durability. There's also a great amount of battery space in it but you may need a new stock. Otherwise, it'll shoot a high enough FPS enough for you and you can always get a tightbore and use heavier BBs for accuracy and range. The R.A.S. is also a good plus. I suggest it.
The SCAR models all have a small battery space which isn't so good. It's also hard to open up and work on. If you do plan on getting one, get the L version so that you can use the readily available M4 magazines.

If you do plan on getting an AK, get a CYMA or DBoys one. If you prefer the look of an AK over an M4, get an AK.

Basically, it comes down to the AKs or the M4. In my opinion, I'd have gotten the M4 just because I prefer M4s.

I hope this helps.