I fly mostly AA, and AS and still end up on DL, CO and NW flights more often then not. I have top tier status on AA and AS and no status with anyone else. For the times that I end up flying on NW/DL/CO, I am thinking about getting a lounge membership with either Delta or Northwest. Is there any advantages to one over the other?

Thank you in advance for your insight---I will also post this in the NW forum.