Sancho,
I think that the two are apples and oranges. They are both intense and short, but I find Z's workouts harder (even though they are shorter). Z's imho use more bodyweight exercises than what I've seen in T25. Shaun is just zipping along like he's shooting the breeze and he makes in look 'easy' but we know it's not. Off course it goes without saying that it's a "polished" workout.
Z's do not seem to move as fast, but I'm sucking wind when I'm finished. When I do T25, I'm huffing and puffing throughout. Cardio is my thing but when you bring in those bodyweight exercises like squat jumps, it makes the sweat pour off of me. I like both of them, but I really love the Z workouts because she struggles right with me and makes me feel like I can and will push through.
I think they both have a place on my shelf. I just alternate the two or sometimes I may use Z as a finisher (since Shaun has me already worked up)
Lesia