I did one topscore, then 3 achievers, one topscore, Kaplan subject tests, one topscore. Basically I used achiever to learn about my mistakes and Topscore as a tool for checking my progress (since a buncha SDNers said that topscore is the most similar to the real thing)
I hope this helped!!
I take the test on the 13th, so I can let you know then how well my prep strategy worked.