Across my varioue bikes I have...
Shimano LX from a few years back - it's OK, nothing more
Hayes 9 - I like em, plently of power and it's on/off, which is the way I like it
Magura Julies - they're also OK, I'm not a huge fan but there's nothing wrong as such
Avid Code 5s, nice and powerful, nice feel, not had to do any maintenance so can't comment on that
Formula Megas - awesome. simply awesome. Huge amounts of power (I can lock my front wheel going downhill if I really want to), no fade, good feel at the lever. I've ridden a lot of brakes over the years and done a fair bit of downhilling and I honest can't imagine requiring any more power from a brake on a pushbike.
Next time I need any new brakes I'll be going for something from the Formula range.