IMO, there’s only a few considerations here:
- Aerie Peak or anywhere else: There’s a very significant f2p community on Aerie Peak (as well as a larger twink community). If you’re looking for a band-of-brothers, this is the place to be. Going somewhere else gives you a much better chance at the Arena Grand Master Trinket.
- A server where you have a current high-level toon: If you’re going f2p, you’re probably letting your main expire, but… every now and then you get free re-tries with your main which you can use to help your f2p account get a few achievements done (you still can’t mail your f2p stuff, but it works well for travel achievements or grinding high-level mobs for items/rep). You also may find yourself renewing your p2p account every now and then for the same reasons. You don’t have that option if you go to a fresh server.
- PvP or PvE server: I’d personally be extra cautious at rolling on a PvP server as you’re never getting above 20 and are just opening yourself up to ganking for the rest of your life. Some love it though.
- RP server: The RP possibilities are a bit smaller on a f2p account because anyone above mid-20’s can’t see your speech. That may be a good thing or a bad thing depending on what you want.