I prefer a pillarless fire rush. I feel that it's the fastest one, but a bit less consistent than, say, a life rush.
For newbies, the best choice might be a Life rush. It's straightforward, pretty linear to bulid and still fast. (upped, it's hella fast).
Maybe it's just me, but I always found the Shrieker rush and the speedbows a bit slower than the two above.