Well do you want an experienced tea drinking consumer base? If so, pick one or two types, especially your own favourites and go with that. Most people don't like buying from a vendor who doesn't specialise because they sacrifice quality for quantity!
Oolong is always good option, but greens and blacks don't seem to be niche market aimed much (perhaps for good reason). Anyways, I like a vendor I can talk to, who knows every single tea and is accessible
Hope that helps! *my vote is green/oolong/puerh/red of medium and high quality