They're both equally excellent yeast manufacturers. You can't go wrong with either.
Both of my LHBS carry Wyeast, so I haven't run into this problem. You could always buy Wyeast from online suppliers if you still want to go with them, but you'll still be happy if you go with White Labs.
On Deck: Jamil's Vanilla Robust Porter
Fermenting: Orange Blossom Mead
Kegs: Element 56 Pale Ale, Ron's Belgian Blonde, Summer'n Saison, Furloughktoberfest '09, Grateful Pale Ale, Sam Adams Cream Stout Clone, EdWort's Apfelwein