I own two WE GBBs, a P226 and a G17. The P226 is from here, and the G17 I had someone buy and make a custom slide for it in the US, then got it shipped over here. I like the G17, I feel that full auto pistols are kinda redundant, as you go through ammo too fast, and if you want to go full auto, why not just use your primary?... However, this doesn't really answer your question.
I can see how the G18 could have issues with broken parts. The blowback on these is rather impressive, and my G17 got its nozzle broken before it even had a full mag through it. It turns out the part was faulty and an easy fix, and since then it's been great. However, I f it was full auto, I could see where issues could arise. I doubt barrels are snapping, but parts of the nozzle or gas chamber I could see breaking, as they are plastic (but decent plastic).
So anyway, it comes down to personal choice. Us here in the forum shouldn't tell you what to get; we shall just advise and complement you on whatever you choose (yea right...). It also depends on where you play, how you play, etc. For CQB, a G18 could work better than some for going pistols only, but going through ammo would be a pain. Also, some sites don't allow full auto only weapons (only CQB sites afaik)
For woodland sites I don't think it would work as well, as pistols lack the range to compete at distance with rifles. I guess a gradual spray upwards could land a hit, but it wouldn't be worth it if that's your gameplan.
One last thing to consider; WE guns often don't fit real holsters. I had the guy I got to do my custom slide make a Safariland ALS holster for it at the time he did the slide. Afaik it's one of two made for WE G17s, but the new Safariland ProFit 578 holsters will fit all modern airsoft guns anyway, so not much of an issue there.