94 celica st: 7a-fe - your options are the A series engines (anything with an "A" after the number) - i reccomend the 4A-GZE because it has stronger internals and comes with a supercharger (which you can swap for a turbocharger if you desire, though i don't know how much work that would be). it also has VVT-I or VVTL-i if i'm not mistaken.
94 celica gt: 5s-fe - your options are the S series engines (anything with an "S" after the number). i reccomend the 3S-GTE (gen3/gen4) engine, swap on a larger turbo, MAYBE a port and polish, a new intake manifold (to stabilize cylinder 3), the apropriate ECU, and a high dollar intercooler.... you're also probably going to want a lighter flywheel and an adjustable cam gear (unless you get the gen4 of the 3S-GTE, which has VVTL-i)...
and ALWAYS get a performance rebuild AND get an engine ballance when finished.
i'm currently upgrading my 94 celica GT right now too, i FINALLY decided on the engine.. 3S-GTE (st205), and just talked to someone back home that will swap it for me.. his cost: beer.... i can live with that..