For the record, I've skied the 08 models of BOTH these skis.
A really tough call.
The thruster is a much more mature ski for next year. Yeah it was a noodley cheap feeling ski, but next year's ski is much more stable, VERY poppy, and just generally more fun to ski.
On the other hand, the AR6 is an amazing ski. This years model is my everyday park stick, and also handles outside of the park very well. Next years is just as good, and personally I like the graphics of next year's model better. It's poppy, stable, and just really fun to ski. I never regret taking this ski out on a given day.
Overall, I think it comes down to whether or not you're looking for all-mtn performance or strictly park performance. Strictly park? Go with the thrusters. Park and All-mtn? Go with the AR6.