Tick determines how fast the server updates, usually in terms for surf a higher tick rate will make you go faster thus usually making it easier.
As for the tick rate to set, considering the engine gmod uses I’d use 66 if you want to go with the default that most surf maps recommend. If you want it to be a lot easier then go with 100. I’d never change from either of those as they’re both well defined in the use for surf.
Only use 64 on csgo. Also it exists, like it exists in most source games, tf2, css, and csgo. Although for most surfers they’ll prefer css as it’s smoother and doesn’t have as many bugs compared to a game such as csgo (when I say bugs I mean ramp bugs and general map issues considering most maps are ports).