Top down: Smith & Wesson, Deringer & Whitneyville Armory --
The S&W was made from the late 1850s into the '70s while the others were minor competitors. The S&W & Deringer were both hinge frames with ejector seen below the barrel although very different in the innards. The Whitney was a solid frame side loader with an ingenious center pin that withdraws for ejector & has a push button latch. It has a side plate access to its innards. Altho the three are of quality construction, I'd give 1st prize to the Whitney for durability & the other two for speed of re-load ---->