It all depends on the size of the ride vehicles. 6 person ride vehicles are ideal for single rider - Millennium Falcon, Radiator Springs and Matterhorn. Downside with those is that Disney prominently displays a sign for Single Rider, so lots of people do it. We did run a test once where my parents had LL for Matterhorn, but my wife and I had just showed up, so we did single rider... standby line was about an hour, so single rider line was pretty long. Single rider ended up taking about 5 minutes longer than LL.
8 person isn't bad - Grizzly River run is great for Single Rider, and not as many people know about it so line is pretty short. I've never single rode Web Slingers, but I imagine it would be fast too. 12 person vehicles like Space Mountain, it doesn't move as fast, but Space Mountain doesn't prominently market Single Rider, so again, not that many people know about it.
Bigger than 12 person vehicles, it's no good. Incredicoaster and Soarin, Single Rider is not great. If Incredicoaster single rider is stretching up on the ramp up to Lamplight Lounge, do not even bother. Standby is likely the same or faster. Soarin is super cast member dependent... if you get one where the cast member is fishing up the standby queue for groups of 3, it moves very slowly.
