Here is a link to a article on this subject:
http://www.offroadadventures-online.com/equip006.htmlLike to ad that the quality of cartridge bearings varies greatly and unfortunately are not always of the same quality as the hubs fitted to! I have a well used wheel with a 13 year old Mavic MTB hub, that I have only adjusted the cone nuts on sins they were new. But a mate had to swap the bearings in his Hügi hubs half way trough the season!
They work much better now with a set of SKF bearings fitted.
There is also great differences in the construction. Some have the sealed bearings(basically a just rubber cover that won´t fight off contaminated moisture for long) exposed while others have a treaded aluminium cover that do seal out grit. Some have the bearings spread wide witch greatly lengthens the lifespan, some are very narrow.
Not included is the fact that also adjustable bearings are serviceable witch greatly enhance the lifespan of these hubs! But it is more fickly and the bearing race can not be exchange.
If you have money to spend and ride lightly loaded or race, I think cartridge is great. But with a low budget or/and going on a long tour, I would get Shimano XT hubs because of the good value, low service intervals ude to good seals, the wider bearings ability to handle side loads and the bigger balls that can take blows better.
