All this talk about grease is fine and dandy, but again, I challenge anyone to point to a bearing failure because of bad grease. The main cause of bearing failures on bikes is misadjustement, specifically loose bearings, which caused one or two bearings to carry all of the load and leads to premature failure of a cup, cone or axle. The second cause is just neglect, failing to repack bearings when the grease gets dirty, but thats not the greases fault. A sand filled bearing is going to fail no matter how good the grease is.

Don't worry about the type of grease, but check the bearings for play often, and re-pack regularly with anything.