At this point in the decision making process, you have probably narrowed your choices down to a final few. There are some more questions you should ask before making your decision.
Who provides the licensing? Some CSPs may allow you to use licensing that you already own. If you do not own the software that you need, will the CSP provide it for you? Most CSPs are able to provide you with licensing for many popular software programs. This is usually done on a subscription basis with a minimal monthly fee that allows you to pay for only the number of licenses that you need installed for your users.
What is their SLA? A Service Level Agreement is crucial in a CSP relationship. This shows that the provider understands that their down time means down time for your business. The SLA should have a guaranteed uptime percentage that you are comfortable with and offer compensation for any outages beyond that.
Choosing the correct CSP is vital in a seamless move to a Cloud environment. They should be willing to communicate with you and answer any and all questions.