[Andy Brockway]

I prefer the shielded over the sealed bearings for our robots because they have less drag. The sealed bearings are better if you have a more hostile enviroment - water, grit, etc.

You also want to buy the correct grade bearing for your application. The unground inner race bearings are cheaper but can handle less load. ABEC-1 or better are fully ground and have higher load ratings. These usually have a bearing number such as R6 (3/8 ID) or FR6 (flanged 3/8 ID)