I prefer the t8.1. I think the co2 in the mag is a better design overall. Every time you reload it's fresh air, so you don't have to worry about running out on your 3rd/4th mag. You can also get a remote air adapter if you wanted too, but with co2 in the mag you shouldn't need one.
I also prefer the looks of the t8.1 better, already come FSR capable, and fits 8 rounds instead of 7.
*Edit: didn't realize this thread was a year old since it was still on the front page...