depends on the course, but if I had to pick three discs for ANY course, it would be:
167g Star Destroyer (pretty fresh)
175g Star Firebird (slightly beat)
175g medium-stiff Wizard (well worn)
However, if I had to go with two discs, I'd trade out the Destroyer/Firebird for a lightly used 170s Champion Teebird, and keep the Wizard in there.
For me, with the three disc thing, I throw both FH and BH pretty equally (slight preference to FH), so I don't need something neutral any farther out than a Wizard (which will go great up to ~250', or up to 350' with some downhill elevation). the firebird is perfect for skip shots, hammers, FH rollers, hyzers, etc... The destroyer is worth having just for the advantage you can get on a lot of holes with a max-D shot, and is great for big, sweeping anhyzers as well as big-sweeping hyzers.
I'm thinking back on recent tournaments, and these were the three discs I used most often. Destroyer left my hand on long teeboxes; Firebird on shorter tees or roller shots, and most of my upshots were with firebirds or wizards.