I have a Proteam Armson 98c that hasn't failed me yet, nice quality. I won that gun at my first scenario so I wouldn't let that sucker go for any price anyways.
I'm not sure that there is any real difference between the a5 and 98c as far as reliablity or quality. With the new e boards for the both of them and the availability of the cyclone feed as an upgrade, it is pretty much a matter of holding the both of them and deciding which one you like better.
As far as the matter of the body kit you choose, Opsgear tends to be really expensive for what you get, Proteam is kind of pricey but worth it imo, specops stuff is OK as long as you know beforehand that it's mostly composite and aren't dissapointed when you get it that it's not metal. Most kits are made for the a5 so if the kitted look is the look you want, I'd say get an a5 over a 98c.
If you don't neccisarily care if your gun looks exactly like an existing model, don't discount the Ion as an option. It's a little harder to dissasemble but with a decent tactical kit and barrel it can look mp40-ish. As with any E-gun though make sure to tape up the grip frame if youre taking it puddle jumping.
Team Aggressive UWL
Loved by most, feared by many.