No Contest - TNT
In early '09 I did what several here suggest - I rented a 600 shift for two days and an XP TNT 500ss (600) for two days as I was in the market for a sled.
I then test drove sleds at dealerships to confirm the rental setups weren't substantially different from the corresponding new sleds at the dealerships.
In my opinon - not even close for aggressive trail riding. The handling on the TNT is far superior. I liked the Polaris engine, and the suspension may have soaked up the very worst moguls a bit better, but for flat out tossing the sled through the twisties and aggressive trail riding the handling of the Doo just rocked.
It was so good I bought the TNT.
I'm not a very manufacturer loyal guy. I'll buy the best sled on the market. I've owned Cat's, Poo's, Yami's and now the Doo.
Of the two choices, and for aggressive trail riding, I'd definitely go with the TNT.
Have fun sledding, and with the newborn!