It's almost always faster to take the shuttle to the ride share lot then to wait for Uber Black to show up at the curb side. The shuttle bypass all the traffic because the LAX buses have their own dedicated lane. Uber Black could take 15~30 min to get in there and another 15~30 min to get out of the terminal loop. I've never had to wait that long for rideshare shuttle and the trip is about 10 min max.