T3s also holds a lot more juice than PT2 mini but the PT2 mini unlike the T3s is able to be fully disassembled for cleaning/drying also you can use your own 510 drip tips on the mini. The coils are slightly different but I haven't had any issue using T3s coils in my PT2 mini.. haven't tried it the other way yet I really like them both
The T3s coil is universal, and the protanks is not.. The base is slightly larger on the mPT, and the t3s is a little smaller. What happens is if you use a PT coil on a T3 - the base overhangs where it screws in, and on the mPT base it is countersunk into the base.
Otherwise everyone else is correct: T3 - More juice, attached tip, plastic body. mPT - glass, 510 tips..
The only other thing I have observed, the t3s base is alot shorter, and the threads are right at the same place the air holes are. So on 'some' mods/pvs the threads will cover the air holes and make it impossible to draw.