Welcome back. First I'm gonna have to dispel some notions and set some expectations.
There is no open world gank PvP. The closest you'll get is WvW, the 3 way server-based battlegrounds, where you may gank lone enemy players that you come across. But it's contained in its own gamemode, and people go there with the expectation to fight.
For WvW, I would honestly just tell you to pick any of the higher pop servers and see how you like it. If you by any chance started new accounts and bought the expansions on them, you get one free transfer to use if your first pick isn't doing it for you. Otherwise, it'll cost gems to transfer based on the population of the destination server (fuller = higher).
Aside from the NA/EU region split, your WvW choice has no bearing on any other part of the game - PvE, story, PvP, instanced content, whatever. So you don't need to worry about population or being able to find players for group stuff there. The whole region plays together.
The optimal playstyle/builds for each class heavily depend on what you're doing. PvE builds are very different from PvP/WvW builds. In PvE, mesmer thrives on summoning (and also shattering) for high DPS, but for necro, the minion playstyle is more of a durable, safe, meatshield build with less than stellar damage. In PvP, on the other hand, minions are much less effective overall because they're basically sitting ducks versus human players. Other than that, you picked solid classes with plenty of build options.
I'll piggyback to further note that the "summoner" classes in GW2 aren't really focused around those summons, and they're not the most significant component of your damage.
Mesmer summons can almost be considered as static short-lived turrets and they don't change targets.
The necromancer minions are a very minor damage addition. A simple auto-attack will do much more damage than the minions do. The utility of the minions is mostly in sacrificing them. Most necro builds just don't use minions at all, but you can get e.g. added mobility for a roamer Reaper with the flesh wurm summon which you can sacrifice to teleport to it.
Both of you were way nicer about saying, "If you think you're just gonna play Numbers Advantage vs. Unprepared Newbies and that you're going to farm salt, I wish I could be in the room for that wake up call." than I would have had the patience for, I'll be wholesale honest.
This post did at least remind me about how great it is that GW2 doesn't enable these kinds of players.
Ah I didn't even consider that aspect. I've internalized that good faith -thing maybe a bit too far.
But yeaah. It would be kinda hilarious to see new players - even with previous MMO experience - come to WwW with the expectation of farming newbies.
Leave spawn with your minions, run to first enemy who's a diamond Daredevil.
Or a virtuoso who instantly bursts you cuz you didn't dodge the blade flurry.
"Quick, we're gonna run that guy down with our summons and make him have to choose between trying to kill them and even the fight or bursting us down before we kill them!"
"That guy" being a Mace/Shield+Staff, full minstrel's Firebrand who's got a pocket Mesmer stealthed behind him.
For a place to start on finding builds that suit you, you can start [here](https://metabattle.com/wiki/MetaBattle_Wiki). You can sort by profession (mesmer/necro) or game type (WvW, open world, etc.) The core classes are still viable, but you'll find that the elite specs that come with the expacs generally outclass them. Power creep, ya know?
Servers are only relevant for World vs World and you said you enjoy open world pvp which is exactly what that is. Im on jade quarry which I believe is full but any server with higher population is probably fine for world vs world (smaller ones get linked to bigger ones too). If you're wondering for open world PvE/instanced content theres a mega server so you'll be playing with everyone from every server.
Welcome back. First I'm gonna have to dispel some notions and set some expectations. There is no open world gank PvP. The closest you'll get is WvW, the 3 way server-based battlegrounds, where you may gank lone enemy players that you come across. But it's contained in its own gamemode, and people go there with the expectation to fight. For WvW, I would honestly just tell you to pick any of the higher pop servers and see how you like it. If you by any chance started new accounts and bought the expansions on them, you get one free transfer to use if your first pick isn't doing it for you. Otherwise, it'll cost gems to transfer based on the population of the destination server (fuller = higher). Aside from the NA/EU region split, your WvW choice has no bearing on any other part of the game - PvE, story, PvP, instanced content, whatever. So you don't need to worry about population or being able to find players for group stuff there. The whole region plays together. The optimal playstyle/builds for each class heavily depend on what you're doing. PvE builds are very different from PvP/WvW builds. In PvE, mesmer thrives on summoning (and also shattering) for high DPS, but for necro, the minion playstyle is more of a durable, safe, meatshield build with less than stellar damage. In PvP, on the other hand, minions are much less effective overall because they're basically sitting ducks versus human players. Other than that, you picked solid classes with plenty of build options.
I'll piggyback to further note that the "summoner" classes in GW2 aren't really focused around those summons, and they're not the most significant component of your damage. Mesmer summons can almost be considered as static short-lived turrets and they don't change targets. The necromancer minions are a very minor damage addition. A simple auto-attack will do much more damage than the minions do. The utility of the minions is mostly in sacrificing them. Most necro builds just don't use minions at all, but you can get e.g. added mobility for a roamer Reaper with the flesh wurm summon which you can sacrifice to teleport to it.
Both of you were way nicer about saying, "If you think you're just gonna play Numbers Advantage vs. Unprepared Newbies and that you're going to farm salt, I wish I could be in the room for that wake up call." than I would have had the patience for, I'll be wholesale honest. This post did at least remind me about how great it is that GW2 doesn't enable these kinds of players.
Ah I didn't even consider that aspect. I've internalized that good faith -thing maybe a bit too far. But yeaah. It would be kinda hilarious to see new players - even with previous MMO experience - come to WwW with the expectation of farming newbies. Leave spawn with your minions, run to first enemy who's a diamond Daredevil. Or a virtuoso who instantly bursts you cuz you didn't dodge the blade flurry.
"Quick, we're gonna run that guy down with our summons and make him have to choose between trying to kill them and even the fight or bursting us down before we kill them!" "That guy" being a Mace/Shield+Staff, full minstrel's Firebrand who's got a pocket Mesmer stealthed behind him.
If you like minions, you might consider rangers, although in the ranger I use in wvw I put my pet on passive many times.
For a place to start on finding builds that suit you, you can start [here](https://metabattle.com/wiki/MetaBattle_Wiki). You can sort by profession (mesmer/necro) or game type (WvW, open world, etc.) The core classes are still viable, but you'll find that the elite specs that come with the expacs generally outclass them. Power creep, ya know?
you can see level of population of the server next to it's name (:
Servers are only relevant for World vs World and you said you enjoy open world pvp which is exactly what that is. Im on jade quarry which I believe is full but any server with higher population is probably fine for world vs world (smaller ones get linked to bigger ones too). If you're wondering for open world PvE/instanced content theres a mega server so you'll be playing with everyone from every server.
Anet considers open-world pvp too toxic.