Verified answer

G&G for sure http://www.airsplat.com/Guay-Guay-G&G.htm

I'm not sure about the Spring but I would recomend the G&G M4. G&G are way more durable external and internal. I owned a JG M4 and it broke after about 2 months. I hope I helped

To be honest G&G is a better manufacture. But JG is not a bad brand either. If your going to go with an upgraded spring you may have to do some internal upgrades. Its just a good rule of thumb, Take a look at this G&G and see if you like it. http://www.airsplat.com/Items/ER-GG-GR16-P-BB.htm

The G&G would be better, and no I don't thin it could take an M140 spring.