1st thing depends your budget.
2nd thing dpends on you HP craving. you want more and more and more.
For the Evo motors, it's the cheapest motor in the market with a cheapest mods list will get you some good #.
Motor response well but it has a limit to it. A cold air intake, boost controler, GMC maf with translater and complete exhaust, FMIC with alluminul piping,FPR and BOV you are looking at 320hp max with stock clutch. with clutch and bigger injectors, your looking at 370/80 whp.
These mods based on evo9. evo 6/7 will have lesser effect gain in HP as they are 220chp.
MKIV Supra are expensive and holds the value better due to rareability. The motor reacts better with exhaust, intake fuel pump, FMIC, boost controller, adjustable cam gears, BOV and FPR. A USsepc Supra will break into 400whp and a Jspec Supra will break into 370/80whp. With AEM and no MAF, USspec Supras breaks into a little under 500whp. These #'s are based on stock Turbos on USspec Supras.
You need a hell lot of more engine internals to support a good size turbos on the 4G63 evo motor.
With just a small turbo on the Supra, ur looking at 500hp minus the AEMECU. With AEMECU, ur looking at 600hp.
So it all comes to how deep your pockets are.
These #'s are based on my experience I'm on my 2.5 evo motor and 1st original Supra motor(mashallah).