Coming back after 3-4 years without playing

Looking at all the servers to see which is the best one to come back to. I'm use to playing an undead Frost mage mostly for pvp and Low ICC boss runs (obs swap to fire for that). Had a few questions about old bugs that were still active years ago. Does deep freeze still not deal damage to mobs/players that are immune to cc and if it works as intended how is it used in pvp (since I've never seen it work as intended).

Might even roll priest this time and let my friend play mage for 2v2's. How's the pvp and raids on horde side? Is it stable on the weekends?