Buying a JDM sports compact is very personal affair. Since you are in Silvia thread obviously die-hard folks here are bias towards Nissan. Here's how the 3 cars stack up generally in my own opinion :
1) Celica : You probably dont like to get your hands too greasy and loath screamer pipes. You may just want to drive for goody enjoyment, occational show-off and feel good factor.
2) Silvia : You are competitive, somewhere inside the wild side waiting to unleash. Relishing power to the limit and the sexy RWD is icing on the cake.
3) GTT : A purist relishing grand touring feel, plush and venerable raw power. Ego stroking uninhibited and ultimately a GTR to die for.
Peace.