systema PTW, then G&P
If your going to buy a super reliable gun that you don't need to fix for more than a season, buy a TM (plastic gun). But if you buy a plastic gun, trust me on this, it's WAAAAAAY easier and less of a hassle to just sell it and buy a metal gun than upgrading it TO metal.
With the exception of the CA sportline, those are pretty easy.
Anyway TM guns keep their value really well since their internals are solid