Reseller accounts should be selected in much the same manner as standard hosting accounts. The first reason to not choose a host is if they offer "unlimited" space or bandwidth. There's no such thing as either of these, and most hosts that offer this are selling beyond the resources they have.

Look carefully at the services and resources the reseller hosting account offers. Some will only allow a certain number of SQL databases, email accounts, domains hosted, and even a certain number of customers that are allowed to be hosted. Pay close attention to ensure that you receive the amount of resource you will need for your reseller business. There are several good resources to check when considering potential reseller hosting companies.... like WebHostingReviewsPlus.com