High intensity interval training with a 1:5-1:8 work to rest ratio. 10-25 seconds on the "work" interval. My modality preferences from "best" to "least best" are as follows:
1) Wingate
2) Prowler/Sled
3) Rower or airdyne
4) Car pushes/pulls
5) elliptical
6) sprinting
7) CrossFit