I dunno I dont use a lot of gimmicks, but I would say TT is up there. Id have to say my distortion gimmick and Daniel Madison Change gimmicks are my fav. This is because I like mind blowing colour changes. That is why Im currently working on a Distortion/DM change gimmick.
Say their card is the 8 of diamonds, you show the 4 and they say no. You say is it close and they are like kinda. You shake it and it flashes into a 6 of diamonds. Then they say nope then you shake it and the pips move to an 8 of diamonds. Will be very hard to make but will probably be my fav gimmick ever.