[Drakker]

For MP5Ks its TM or a very hard to find full metal proline Classic Army. Everything else is either super heavy and difficult on magazines (Cyma), made of cheap plastic (Galaxy), or weird and crappy (Cybergun GSG series). For P90s you can make do with a King Arms, but the hard to find Classic Army proline is also excellent. Marui's P90 is great for CQB, not so great outdoors. Reviews of the G&G P90 have been mitigated at first, no idea if the newer versions are better. Cyma has come out with a P90 recently, no idea if its any good. AUGs are all crappy as far as I know. The fore grip WILL break on all of them except the high-cycle TM AUG because it doesn't have one.

Don't bother with upgrades too much. You have to know what you are doing to get good results. For most people, swapping the hop-up rubber is really all that's needed. If you bought a very low end product and you suspect the inner barrel is really bad/defective, you might want to change it, but a good barrel will cost you 100$+ with the current state of the Canadian dollar, and you might not see much improvement in accuracy and range. Most of the time, upgrading the inner barrel is hardly a good bang for the buck. Don't bother with cheap upgrade barrels, they all suck and are likely worse than your stock inner barrel. Go quality or keep your stock barrel.