It depends on the year as the early one's were SKF's made in Sweden (Original Volvo company made) Around 1988 the bearings were made by a Japaneses company KOYO IIRC, and the last time i got them from a dealer that's what they were. The Japanese bearings are wide range in quality, Koyo is usaully very good, and so is NMB. The US bearing manufacturers that are superior are Timkin and New Hampshire Ball Bearing, who supply most of the NASCAR and racing bearings, and who is also owned by NMB of Japan, but most of these will cost more than going directly to the Volvo counter. Even the SKF brand which is now made in the US cost more than Volvo list if you buy from a distributor.
If you buy from an autoparts supply warehouse like World-Pac the SKF is probably the best choice, but will be only slightly less than Volvo. IIRC the going rate for individual bearings w/races are ~$20-$35 each x 4 = about what Volvo charges.