Custom. You get what you want, how you want it, in what shape you want it, how fast you want it, and so on. It's more expensive, but I've found it to be worth it in the end. You end up (in my experience) with a lighter package, and you know EVERYTHING about it, so maintenance is pretty simple.

Oh, and you get the bragging rights of a custom system.


EDIT: If you have ANY kind of a budget, I can't suggest anything other than Andymark gearboxes. They're reliable, proven, light(ish), and the best bang for your buck. They're not as durable as I'd like them, but I personally prefer bulletproof (figuratively) robots.