If the quality is excellent and the name isn't tacky (e.g. for Dummes), then I think a series is much more beneficial. There's no way I'd compare '..for Dummies

If the quality is excellent and the name isn't tacky (e.g. for Dummes), then I think a series is much more beneficial. There's no way I'd compare '..for Dummies!' books and StackExchange on anywhere near equal footing.