No question about it. The Lighthorsemen. None of the "hurray for Hollywood" bogus stuff about horses. (e.g. no feral horses suddenly being well trained and conditioned the first time they're ridden; no horse doing the impossible for the love of someone; no horses making a run that simply isn't possible; performing impossible feats, etc, etc, etc,..
(for those who never saw it):
Based on the actual attack of the Australian Lighthorse on Beersheba during WW I. More accurate than most historical movies (not quite accurate on who actually believed and who doubted the false intelligence...not sure why they reversed it), but mostly extremely accurate with the horses, what they did, how they were used and how they performed.
The charge on Beersheba scene was incredible. Showing each progressive stage from deploying, advance at the walk, advance at the trot, advance at the canter and then charge. Complete with the drawn bayonets which is what they actually used.
The era of Cav had was ending, but that battle was one the examples of why the army should have kept mounted Infantry (although it wasn't US mounted Inf, but Australian....the value is still the same). They did realize it again during Afghanistan. There are still conditions where mounted troops are the best choice, but once it served it's purpose they disbanded it again.