They work OK on mine - and it has pretty low springs at the moment (unsure of brand, they came with the car). That said, unless you're crazy about the "active" nature of the TEMS and love to hear them switching between hard and soft etc go for the Koni setup.
A properly setup spring/shock combination like the Konis will handle a bit better than TEMS (new TEMS shocks are reasonably priced) but be quite a bit more expensive. Depending on what driving you're doing in the car should colour your choice as well - long trips on shit roads seem even longer with a nice hard set of shocks in the car!! (and the road will seem shittier as well)
Still, with TEMS the back of the supra is a bit soft for hard cornering etc.
And I don't want to hear any comments about Supra's being "straight line weapons". Despite their porky weight they're a lot of fun around corners too, and handle magnificently, esp fast, long sweepers!