The best hosts coming from someone who has been developing and running garry's mod servers for around 3 - 4 years now it'd go in an order similar to this: 1) Hexane Networks - Hexane Networks has a reliable owner who helps you instantly when you need it, When i thought my server was under ddos it turned out to be a server issue which was fixed in under 5 minutes, The prices of the servers are cheap as well. The support tickets are answered decently fast which i always like about a host. 2) Crident Networks - I especially love the Backdoor Scanner and Workshop Downloader on this host, This helps me so much making it easier for me to remove backdoors and making it easier for me to get addons onto the server. Support Tickets for me have not been answered fast and the prices of the servers are decently expensive. 3) Nitrous Networks - I use to use this host before I swapped to Hexane as I thought their servers were decently well ddos protected and decently cheap, They offer you a free web host when you buy a Server which was always great as I didn't want to use something such as Enjin or Mistforums, This is why I rate this at number 3.
I don't think many of you will agree with this list but its my personal opinion.
Also, If you ever need help developing your server AligatoR hit me up, I can always help (This also goes to anyone that needs help)