I have a friend who teaches swimming to kids trying out for the Navy seals.. he does a variation of the sidestroke that seems to be very low energy and somewhat speedy...
I did that stroke for years while in the Navy. In tri it can be a great "rest" stroke but if you do it properly (mostly legs) it is not good for setting up the legs for the next events. If you can crawl that will serve you best, but if injury prevents crawl...CSS is a great alternative.