Gemtech is really top notch stuff and their customer service is second to none. AAC is also quite good, but they recently had a steep price increase and I've heard a few complaints about their customer service. SWR also makes excellent cans though I've not heard anything (good or bad) about their customer service.
Personally, I'd recommend you start with Gemtech. Their products are very good and if you ever have a problem you can rest assured it'll be taken care of quickly and professionally. I don't own a Gemtech can, but a good friend of mine has two and anytime he's called Gemtech with a question or problem Doc Dater answers the phone himself and takes as much time as my buddy needed.