There is no doubt in my mind that publishing house books have less typos and grammatical mistakes than self-pubbed books. Authors who self-publish sometimes rush through edits. Top publishing house books also have editors who point out lagging scenes and suggest rewrites. Another advantage is marketing. Going with a traditional publisher still requires the author to promote a book, but the publisher shares marketing methods, expertise, and may gift the author for this purpose. Authors who sign with the same publisher band together to promote through rafflecopter and twitter.
I think it's fine to ride two horses at the
same time. Because it take longer for a novel to go from proofing to publication. Here is what I do-- submit longer books, novels over
50,000 words, to my publisher, but I self-publish novelettas (10,000 and under).