I'd probably opt for SuperShuttle
I have taken them from DL to LAX and not had any problems. You may (actually, you probably WILL) end up sharing a van, and may have to stop at other hotels along the way, but it really doesn't take too long in between.
When we rode to LAX from DL, it took about an hour to hour and 15 minutes to get there and that was WITH stopping at 2 other hotels along the way . . . and having to wait for the family to get ready at one of them.