Cartridge Bearings versus Cup and Cone Bearings
I noticed that SRAM uses cartridge bearings in their hubs and Shimano uses the traditional cup and cone bearings. I always thought that cartridge bearings are superior in terms of rotation smoothness but Shimano must have a different opinion.
Is there any difference in these bearings in terms of rotating smoothness, reliability and adjustment?
Shimano Dura Ace hubs are the smoothest hubs on the market. Bar none. Cup and cone.
Easier to maintain, but not as well sealed. Also, if you wear out the cup, the hub is toast. However, this is very hard to do, and you'll definitely notice it beforehand.
Cartridge bearings are "the standard" these days, for better or worse. SRAM is hardly at the "high end" of the spectrum, hub-wise, and I think a DT, King, or other high end cartridge bearing hub would serve you better in the long run. Pros for these are long service life, and a certain amount of weather resistance. Cons are seal drag and on some, finicky bearing preload adjustment.
Personally, I used old school DA 7400 hubs on my road bike, and DT 240s on all of my MTBs. 240s are the most durable hub on the market in my opinion, and roll better than the other cartridge bearing hubs.
Shimano and Campagnolo are pretty much the only companies making quality cup and cone modern hubs. And they are some of the best out their in terms of durability, pretty competitive on weight if you keep the exotic stuff out of the conversation.