What's your max budget for this?
Note: Since you're using to make money, the you should match your phone bill budget (~$50), not your Taco Bell lunch budget (under $5). Given that sort of monthly amount, I can help you find something BOTH excellent AND under budget.
What you really need is "reseller" hosting. Understand that it has nothing to do with "reselling" anything (and I hate the term), and it's simply more than multi-account + multi-domain hosting. 1 domain per account is what you want. Trying to cram 15 sites into a single cPanel/Linux account as puny "addon" domains is a performance issue (slow sites!) and a security issue (one site is hacked, all sites are hacked!)
So for reseller,
Stablehost is indeed a top choice. I would also look at
Veerotech and
Site5.
What countries are these sites targeting? That will help narrow it down.