I've been sticking to single leg exercises for a number of reasons:
- closer assimilation to cycling,
- increase in stability,
- easier to self spot,
- less equipment!
(e.g. single leg squats only require 2 x 80 lb dumbbells)
However, I am realizing there is much greater eccentric strain with the slower controlled lowering and stopping. It's also impossible to do a bench seat stop with single leg squats. This might be a contributory factor.