Confused about various zones.Follow

My GF and I play together and due to our style of play, never group with others. I am a 17 Sorcerer and she is a 17 Summoner. We are evil and currently hunting in the Commonlands.I know that the next step up would be Nek or Thundering Steppes. However, I have been hearing about a lot of other zones but have not found a good list of what level the various zones are and if they are only group(3 plus) etc. Any info about links to a list or ideas of where to go when would be great. Thanks