What are the features I should be looking at when considering a hosted CiviCrm environment? Are there red flags I should look for from a vendor? There are a number of vendors out there all claiming to the best/fastest/most supported. Prices range from $3-$20/mo so how to choose?
Much could be said on this (and probably will be!) but here's a few starters you might want to consider. What is "best" for you depends on which factors are important for you.
If you use a hosting environment that specifically supports CiviCRM then things like MySQL version, MySQL permissions, php version, php memory will be ok. Otherwise, you need to check they meet CiviCRM's requirements which are fairly demanding.
Some hosters will upgrade Drupal & Civi for you. On others, you manage your own upgrades.
Some provide Let's Encrypt automated free SSL certificates.
Some provide ssh access. If so, do they provide drush, wget, git etc? (Does drush, wget or git matter to you?)
Personally I'd opt for a specialist CiviCRM hoster. Avoid a hoster that doesn't explicitly mention CiviCRM.
I can't resist adding that with a cheap host, you'll probably get what you pay for, but only if you're lucky. And as the old Bell bicycle helmet commercial used to say, if you have a cheap head, buy a cheap helmet.
So: what is your data worth to you? And how much is it going to cost you if something goes wrong? Not just issues of performance and availability, but also security and privacy.