There are a few different air filters available for the MkIII Supra Turbo.

They were reviewed by RevSpeed which is a Japanese Tuning Mag. The full article can be found here, but here is a summary along with pictures of what the filters let through.

Apex Super Intake : +14BHP : Filtering Performance: Excellent
K&N Filtercharger : +13BHP : Filtering Performance: Good
Sard Sports EX : +11BHP : Filtering Performance: Fair
Blitz SYS Power Core: +13.9BHP : Filtering Performance: Poor
HKS Super Power Flow: +13BHP : Filtering Performance: Very Poor

As can be seen the one to go for is the Apex Super Intake, or for convenience of getting hold of one the K&N. It is highly recommended that you steer clear of the HKS filter and if you look at the crap that it lets through compared to the others, you will see why.