it's tough to rank relays without a bit of redundancy since a lot of actual functionality still depends on public relays in my experience. I went through and used each relay, with one or two public relays to keep things going, on amethyst and observed how my followed feed and global feed changed. I also tried several of them on gossip.

my main factor for analysis was looking at the posts on my global feed that I determined (arbitrarily) were high quality and noting which relays they came from. this means the relay's quality also depends on the user base of the relay, which is one of the most important aspects of a relay imo.