A great low cost option
The Enduro Abec 5 LLU bearing is a great low cost upgrade. Featuring a high rated Abec 5 bearing, with a deep groove for extended bearing life. High precision balls are within 5/1,000,000″ round. These are military level specification, used for precision equipment. R-64 hardness, of the highest grade.
LLU is a full contact, dual lip seal riding in a groove on the inner race. With more sealing pressure, these are ideal for wheels or headsets that continually come in contact with dirt, sweat, and dust. The increased seal pressure and 2 lips help retain the 90% grease fill used on the bearings to better displace any moisture and continually lubricate the balls and races.
The Enduro Ceramic XD-15 is as good as you can get. We spent years refusing to stock a ceramic bearing, yet testing out dozens of brands. The one thing we always found was the bearings were a lot more expensive (of course), but because of corrosion issues the bearings would need to be replaced much more often.
The new XD-15 bearing from Enduro actually gets better with age. With oversized Grade 3 Silicone Nitride balls that actually polish the races. Enduro has gone so far as to offer a lifetime warranty on the XD15 bearings! That is unheard of for a wheel bearing and just one of the reasons we finally offered a ceramic bearing in our wheels.