I did some serious research before picking T25 over Insanity and ultimately picked T25 because it would enable me to continue my other workouts while I did it, and if I felt it was too light I could double it up. The T25 vs. Insanity comparisons I read said they were basically the same stuff, just T25 was shorter and if you wanted to stretch it was not included in the '25 minutes' (though there is a 3-4 minute stretch-session following each workout if you have time.) Pretty much everyone who did Insanity first said T25 was cake because it was just shorter.
Personally (I'm three days in) I find the cardio fairly light, the lower body/core-work a bit of a challenge (but doable) and the upper body stuff just brutal. Honestly though, that's just me. I'd been ramping up cardio a lot lately and other than push-ups here and there don't work my upper body much at all. Not sure that helps you though.