I have both chargers that I got from xheli.com, and have had them for nearly a year. I bought the Thunder T6 first (because of price of course). But when you add the AC adapter it actually is a little more than the AC6. The T6 is very good, however the reasons I would get the AC6 are these:
1. The adapter for the T6 is large and seperate, thus you've got two parts where as the AC6 is one complete piece.
2. The T6 has a built in cooling fan which runs wether its cold or hot and will eventually burn out (although mine hasn't yet and I pretty much use it every other day). The AC6 is inter-cooled (much like a car amp) which prevents it from overheating.
3. ALL the programming for both are identical and very easy to use after a few times and using the manuals for reference along with some common sense. It's pretty hard (damn near impossible) to charge with wrong or incorrect connections. Your batteries are safe.
4. Both chargers beep when the charging is done (you can choose to turn the beeping on or off), however, the AC6 is TWICE as loud which is very helpful if your not watching it all the time.
5. Last but not least is important. The AC6 is "Dual Power". I have set the same charge/balance techniques with both chargers using identical batteries (11.1v, 2200mAh 20C and some 7.4v's) and started charging at the same time. The AC6 is done 20-30 minutes before the T6. Important if you love to fly but hate to wait! Just my opinion.