I've got a whole mess of relays I'm connected to after a lot of trial and error of which were overloaded, check them out on my profile!
I removed a lot of the "default" ones like relay.damus and relay.snort as those just get overloaded by the hordes of people that just use the 5 default relays that come with the client. Those default ones have become unusable at this point.
Also, it can be handy to check nostr.watch every once in a while and see which relays have uptime closest to 100%