Very new here, so I'll leave the weighty ideas for those who have been around around longer, but both me and @Nadalyne did experience trouble creating characters on Mateus recently and I do see the occasional short log in queue, but nothing major.
I don't have a huge stake in either choice and we'll likely follow the guild if a transfer is decided during the free period. Wherever we end up, I want to echo approval for a server with a population of the bigger side. I've done the low pop server thing with WoW and SWTOR and I do enjoy having a healthy population to play with. The two of us do tend to be more involved in PvE stuff, but I do like the occasional RP interaction. As long as we can do stuff like that, we're down for staying with whatever RoH does.