Nagafen's lair for a 40 pally ?

[Iphice]

40 is plenty high enough to find good groups in SolB. CoM is also a good option although it can get super crowded during peak hours. I am not a big fan of soloing on melees because I tend to get bored but you can solo in either of these places if you want or go somewhere open like DL, all depends on what you like.