It depends what you want to fight against:
SFR (International) best over-all coverage and often the biggest blobs
Desolation (International) strongest night team, 2nd best coverage
Kodash (German) strong primetime, lots of roaming teams
Riverside (German) zone wide blobs, strong siege
Gandara (International) strong primetime, lots of roaming teams
All of them are very high population besides Kodash. If you want to fight against the biggest blobs in EU, I suggest you will move to a server which often facing SFR. If you want to fight against enemy roamers and gankers, then play on a server which is often pitted against Kodash and Gandara. If you do your selection with opposite logic, you might soon come back to forums and complaining “oh by the enemy servers don’t have much any roaming teams… first it is 1 vs 1, then they come back with 10”.
If you plan to play on many different hours and on NA hours as well, then going to the servers which have coverage is a good idea. Fighting with just 1-2 guys against enemy server’s big night team, might not be fun.
I know that my server, Desolation, has the reputation of being the biggest PuG/militia server in EU (plus being the pve capital of EU in the days before megaserver), but I think things have changed. I would give gw2 gold us zone wide PuG blob crown to SFR, which is obvious #1 choice for bandwagoners. Desolation has gotten an influx of new guilds. Many Desolation guilds now run closed raids and Desolation has become a guild heavy server. But when the Fall Tournament starts the pve people will also flood in, unless they all enjoy EotM. Our night team + many others are now taking a rest before the Fall Tournament, thus our ranking is tanking.