For my the products I design, I have used and would use again NMB, NSK and SKF bearings. These are all ball bearing assemblies. For the vast majority of applications (including bicycles), even so called "cheap" Chinese bearings are more than adequate if they are properly lubricated. For non-competitive riding, an automotive wheel bearing grease will keep your bicycle bearings happy for thousands of miles. I suggest solvent (70% isopropyl alcohol is fine) cleaning the balls, raceways, cones, etc, drying then immediately apply the grease to all the metal surfaces inside the bearing system. Use nitrile gloves - your finger oils are bad for bearings.

Joining this thread a little late, but I thought as a Mechanical Design Engineering; I could contribute some useful information about ball bearing materials.

Why ceramic? well on bicycles, weight but mostly marketing - I'd say 1% weight, 99% marketing. Ceramic balls are used in high speed (10,000 rpm and up) very high precision applications, with very careful match of thermal expansion coefficients (CTE). They must be properly (and usually very highly) preloaded; and must always be under compression. Impact loading which results in a loss of compression will destroy the ceramic balls almost instantly. Ceramic expands less than steel - and much much less than aluminum with increasing temperature. As alluded to above, they are not very good for low speed applications (all bicycle applications are low speed). If you are professional road racer, and your mechanic adjusts the timken bearing preload every day based on the expected ambient temperature - they are okay, and may be worth the weight reduction. If not, they will not last very long. The pro does not care, as they will be replaced at least every week.

Steel is great for bearings; 52100 is the most common bearing steel, it is very hard and very tough. Not as hard as ceramic, but much tougher. It will handle shock loads quite well. 52100 needs to be well lubricated to keep out moisture as well as to function properly as a bearing. 52100 will rust. 440C (and some proprietary cousins) is the most common stainless steel nachi bearing material. It has much better corrosion resistance than 52100, but under extreme environments, it too will rust. 440C is not as hard as 52100, and has similar toughness. Steel bearings are more forgiving of the thermal expansion mis-matches than ceramic.

Bicycle bearings should last for years and provide you with thousands of miles of travel---but they won't last forever. In some cases they even fail completely if they haven't been maintained correctly. Part of a maintenance schedule should include replacement of wheel skf bearings before they fail. The procedure isn't that difficult if you have about an hour and a few small tools. Front and back wheels are similar in procedure to change bearings and only require slightly different tooling.

An important aspect of bicycle maintenance is to grease the bicycle bearings. This helps to avoid costly future repairs and give you a much smoother, more comfortable ride. The wheel bearings are between the cup in the wheel hub and a cone screwed to the wheel axle.

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