Any server provider should be fine where you reliably get the needed performance that your configuration and your amount of concurrent users need. I suggest you to take a look at this page to get a list of requirements that usually are required for something between 100 and 200 concurrent users with a typical configuration:
This page also mentions some suggestions for vendors and samples of server sizes. Those server sizes should give you a good estimate of what to look out for.
I suggest choosing a server provider that has very good network connectivity with lots of peerings to internet service providers in the region of the majority of your users, and which also buys decent amounts of transit from a Tier 1 internet service provider. This is necessary to avoid network congestion (-> high amounts of packet loss) during peak internet traffic times.
For requirements and best practices of Moodle, please take a look at the official Moodle documentation.
Best regards,
basisbit