there is an issue if a server is left running the same map for a long time ( i.e at least 1 day ) where it appears choppy to play on, this may be what you are describing - the owners of those servers should either restart them or change the map once per day if possible
edit* for reference try my server @ pub.tf2nerds.com there is an issue with the control panel for the hosting whereby i cannot get a nightly reboot scheduled