Gas Gas Gas ! I pretty much only run GBBR's now. I took my aeg AK to the last game day and even ran it for a game, but it just felt so 'Meh' compared to the gas ones.
Mine are a mix of brands, I have several WE's and a couple of VFC's ( there is a DE Noveske under the tree for tomorrow) . I never feel out gunned, just adjust play style to suit and then double tap the spray and pray bunch . I generally run 5 or 6 mags and a speed loader for a game. 2 plus BB lodas to a gas fill gives me between 300 and 400 rounds which is ample. Heavier BBs work well on GBBRs, I run .30's for a good compromise on weight and cost, but they will all happily run heavier.
Playing in cold weather just requires good mag management to keep them warm. I use green or red gas in them depending on temperature, although the VFC M249 now runs pretty much exclusivly on CO2 .
Maintenence wise , they are simple to work on and it's usually just a strip , lube and barrel clean after a game day.
Mine have all proved completely reliable , I cant remember having a failure that wasn't my own fault.
No AEG will ever offer the level of imersion that a GBBR does, but you have to want that play style.