T3 hands down.
My reasons: You don't feel any different, except that you have a bit more energy and clarity. In fact, you just wake up 3 weeks later and you're like holy f*k!! What happened to my waist, I'm swimming in my pants
Clen - you feel like you're doing light cardio all day, prone to headaches, its illegal for humans in lots of countries for a reason (not without prescription, but for humans)... its not nearly as safe (you can definetely overdose) and its just not worth it. I mean, throw in an IF here and there and you get the same results much faster.
t3 is more like a supplement, I mean you really just supplement your natural system
clen - bah