Currihane2

The OP didn't mention if he usually does woodland or CQB but here's my thoughts on GBBR's. I have a few:
GHK SIG 552, GHK AKMS, TM AKX, VFC M4A1, VFC MP5SD, AGM M4, WE PDW, WE SCAR L, WE M4 CQB, Marayama ACP9K G Pro, TM MP7 x 2, KWA Scorpion, KWA Mac11, TM Siaga 12K and a Beretta SMG from 1987 which is more of a wallhanger. I did have a TM MWS but sold it a while back when I fell out with GBBR's but now think I need another or the DE clone. I've also got a couple of the GBBR 10/22's but I'll discount them from this waffle as they are set up for sniping.
I don't use GBBR's at woodland sites during walk on days simply because I'm outgunned or more accurately out ammo'd. I tend to use my TM recoils, KWA T10 or GBLS on those days and get a similar level or recoil to keep me happy.
When I use GBBR's it's mostly CQB sites and I don't run anything over .28 tracers as there doesn't seem to be a need. If I need more range the  I just get a bit closer. I tend to carry at a minimum 6 mags when using GBBR's as anything less means I'm half fighting and half reloading after running away.
I also carry at least one pistol speed loader and a fake grenade that is actually a gas can so I can top up my mags if needed.
 
I've fired quite a few RS rifles over the years and I'd say the recoil on a GBBR is similar to a 22 LR round. Some GBBR's do a better job of increasing the realism, for instance, the TM MP7 has the bolt smashing into the rear, right next to your ear and this increases your perception of the noise from firing but to everyone else it just sounds like a GBBR.
Firing hot can be an issue and I've found that using the Vorsk gas either number 6 on hot days or number 8 on colder days gets me through the chrono without issues. By using the different numbers I don't need to worry about fitting Npas's although in the WE GBBR's and 10/22's I've fitted Npas's.
 
Looking at reliability, the TM GBBR's all work perfectly if kept stock and you want to use up to .28's. If you decide to go for heavier ammo then you go into the modding world and it can go either way until you hit the right combination. What works for some people doesn't always work for others.
My GHK's both work very well stock and I'd put them as the same reliability as my TM's. Some people have had issues but my only issue has been with the GHK mag base plate falling off and loosing a spring and follower which was $8 to replace but still a pain in the arse. 
My VFC M4 again works all the time and it's a Gen1 version and I bought a bunch of spares, ready for it to collapse in a heap but I haven't needed to use any of the spares yet. The MP5SD took a bit of work and aftermarket parts to get it firing consistantly but now it's a steam train.
I've slated WE GBBR's before and all mine are Gen 1 closed bolt version and work ok'ish in good weather but the Mags are a terrible design. It's a clam shell design with the worlds biggest square o ring that you will need to eventually fill with silicon and wait 24 hours to see if it still leaks. I wouldn't recommend WE as a first GBBR simply because you could come away with negative feeling about GBBR's at the end of it.
My KWA scorpion is awesome and the MAC 11 will either work fantastically or vent all the gas depending on how it feel that day. 
 
I'm not sure if anyone else has mentioned maintenance but GBBR's require cleaning now and again to stop the working parts getting gummed up from dust, twigs, leaves, bits of chopped BB's etc. It's good practise to wipe the bolt and upper recess where the bolt travels down and re-lubricate along with cleaning the barrel and hop up chamber at least every couple of games. Just like the RS versions, grease attracts dust etc which can effect the function of a GBBR.
 
I was going to mention that the Marayama ACP9 G, the MPX and the up and coming ACP9 are all excellent little SMG's with the Marayama taking 50 round glock mags but you will probably end up buying a MWS