1. Best server in reagards of what?
2. It's also very much a matter of personal taste, so you will have to answer it for yourself mostly.

I don't know anything about a rating for servers.

And fun in the game depends on more things than I could even mention here. I can't answer that question for you, nobody except yourself can do that.

If I were you, I'd start by working out what you want from your game and what you already have:
I mean if there is one server where you already know somebody and you want to play with that person, go play there.
Or ask yourself the question if you prefer a protected and newbie-friendly environment (-> pve servers like bohemia or grail) or a if you're looking for more player vs player action (-> pvp servers).
If you're interested in playing in a historic environment with authentic maps, go for outremer (-> Mediterranean Sea map) or britannia and albion (-> British isles and nordic map).

[...] and so on and so forth ... etc.

PS: Try looking into the statistics, too. Maybe that helps.
http://1100ad.com/de/library/statistics

Quote dpopovic:

This is the answer I was looking for thanks

That's funny, but anyway, if you're happy with my answer everything is ok.

Quote dpopovic:

What is the difference between PVE and PVP?

pve = player vs environment (You will find more adventure huts and more protection from other players aggression. For example, war pacts need to be accepted.)
pvp = player vs player (less adventure huts and more emphasis on battles between players; far less protection from wars and takeovers)