The P321 hubs (front and G2 magnetic driver rear) I have are nice, but don't "
do" a lot compared to any other decent hubs aside from saving a few grams and being quiet. The number of points of engagement is impressive, but definitely not necessary. The original freehub seal mine came with leaked like a sieve, but an updated seal mostly fixed that. I did have one of the pawls lose its magnet (and destroy it), but that was before I got the updated seal. I suspect I ran it mostly out of oil without realising and the adhesive that holds the magnet in let go. To the hub's credit, nothing was damaged (ie: the drivering was undamaged) aside from the magnet being turned into an ugly metal/oil puree. I'd buy again, now they have the updated seal, but mostly just because they're light and have ultimately been quite reliable due to good customer support (through Cyclinic at the time).
Hopes are kind of agricultural by comparison (engineering-wise), but that's a good thing IMO as they're really easy to work on. In terms of ride feel, they hardly feel any different than the P321's other than a more aggressive feeling engagement, and being buzzier. I've had a few Pro-4's I've bought from new now, and they were annoyingly inconsistent in terms of rolling resistance. Was never sure what it was that caused it until I bought a Microspline freehub for one recently. The new freehub had a identical looking but very different feeling seal on it. The new seal was much harder, but doesn't drag against the hub body anywhere near as much. It's now the best rolling Hope rear hub I've had to date.
Onyx are meant to be the be all and end all of low rolling resistance, but as
@rstim mentioned thay comes with a significant weight penalty. There"s also some mixed reviews of the newer Vesper hubs over on MTBR. Presumably these were early production hubs, but there was some really basic fails in there (freehubs falling of with cassette attached if you have the wheel out and tip it to the drive-side, slipping sprags...).
One other option to consider if you're going to save for something flash is Chris King. It's a bit like suggesting someone buy a Yeti, but they are bloody nice hubs. A mate has them and
damn, they roll so nicely - noticeably better rolling than my P321's sadly. The P321's aren't boat-anchors by any means, just the CK's roll insanely well. I get the impression they have a bit of a patchy reliability record, but his have been faultless. They sound great too. Bit of buzz, but fairly muted.
Haven't had enough time on DTs, but rolling also seems good, 36POE isn't heaps but they seem to engage smoothly if that makes sense, so they use what they have well.
Or alternatively, just lace lighter rims onto the hubs you have now. Rims are where you'll feel the performance difference anyway. Talking about the subtleties of hubs is for twats on the internet... Oh, wait... Oops.
