From what I can tell the biggest hurdles with stadiums are where does it go, what does it look like, who pays for it, and how do you get the land, with the last two being the most important.
So far, LA has all of those figured out, if you assume the stadium they drew up is the one they want, which isn't certain at this time. St Louis has 2 out of the 4, if you assume what it looks like stands (which is doubtful), but the last two are up in the air, which is big. At this point, unless LA is a big bluff, St Louis definitely has more hurdles. The problem is while Stan seems willing to put up his own money in LA, he's not in St Louis, and that makes it much harder for them.