I would buy the one you really want. Its great finally getting the gun you've lusted after! Then upgrade all of them. Then buy the next "gotta have it" gun. Its a viscious cycle.
Just buy a new one. fixing up one doesn't give you the same feeling. I know, I got a couple hun'ert I'm gonna upgrade some day but I just keep buyin' a new one every so often.
I enjoy a new gun as much as the next guy and I don't buy "wall hangers". I have a few that I've kept in their original shape to keep the value up. Most of mine are modified to fit me better or a special need. I like tricking them out.