A daughter board with properly tuned eeproms is the way to go. Piggyback's are good, but you really need one that will do ignition timing modification also, and i wouldn't touch a unichip with a 10ft pole.
That only really leaves a few units, the Pefect Power SMT6 that i'm currently using, the new SMT7 and the Greddy E-manage. A new version of the Emanage is coming out this year apparently.
You're not going to see the gains you're hoping for with only an airfilter change and modified engine management. You really need a full exhaust and cams.