A managed dedicated server should be good enough. If you select a reliable company like liquidweb, nothing much to worry. 100 small websites on a good server is not a big deal.

Reseller accounts is not bad, if you really dont want to own a server. You can get an account with hostgator or something, you know they will not run away. I would recommend a small host named hosting matters too. Had a nice expereince with their reseller account some 4 years back.