Sloan didn't say she was waiting for Don. I took that as her telling him that he missed his shot with her.
He asked why she was still single and she responded "because you never asked me out". I took that to mean that either she was waiting for him or that he set such a high bar that no man could compete.
Remember the context of her saying this, thinking she is not going to be around him any more. Either way, I don't see it as being nearly as creepy as Whitford's character stalking Peet's character on Studio 60. I do wonder if Josh and Donna weren't together until near the end of The West Wing because it was better for the show or because Sorkin didn't know how to make it work.
The Whitford thing was restraining order creepy. Sloan is the hot girl who crossed the line from quirky to unstable.
Maggie is my favorite of the bunch, but "blond girl next door" is pretty much exactly my type (even though I never end up with anyone that fits that description). They did make Lisa more desirable when they showed her at work. That took a little of the drunk skank vibe away.
And, FWIW, the Josh/Donna relationship was a great story arc. You'd get about five or six moments a season for the first five seasons that pushed that story line. It was so carefully done that the payoff was really nice. West Wing in general played all its romances a little lighter than Newsroom. The CJ/Danny thing was slow and careful. Charlie/Zoey, too. ... Rarely were those even the second storyline of an episode. (Sometimes, but rarely.) Usually they were down the line a little bit further. Maybe that helped.
One common thread to all of those relationships is that the characters did not get together to stay until after Sorkin left the show.
There are some excellent pictures of Olivia Munn out there and 1, allegedly, special NSFW, pic. Kelen Coleman, Lisa, is also seriously hot.