Best move is going to be to look for a host as near as possible to your client's market. Make sure its not just a one man show running the company or that support is on the other side of the world. During the day you'll have to wait a 8 hours for a response. Local support is the best. Also avoid all hosts who offer unlimited databases / website. A sign of overselling and heavily loaded servers. Best of luck with your ongoing search.
Current one is rude (support), slow (ftp) and buggy (control panel)
Sorry to hear about your current host. Can you let us know your existing host so that it can also be helpful for someone searching for Windows reseller? Additionally, most professional hosts will be providing you with 24x7 technical support with around 1 hour response time (by human). I'd recommend you to drop in tickets at some odd hours in night to check your prospective hosts response timings and availability.
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