IMO, Harris, no contest. Unless you're a real budget-minded individual, I don't think the knock-offs are worth considering. Unless you want to use something quite different, like the GripPod (not for me, but YMMV). Or go upscale to an Atlas. But the Harris is solid and popular for a reason.
There are really not that many options to consider when choosing a Harris model: Length, pivot, and adjustment style.
Length really depends on you and your shooting style. The short one is probably too short to be useful for field shooting for most people. It depends on how your typical COFs are set up, too.
Personally, I opt for the pivot models for general versatility, but there is a case to be made for the simpler and cheaper non-pivoting models if your COFs always feature level surfaces to rest on. If you get a pivot model, the extended "quick throw" pivot tension lever is a great addition (aftermarket only, I believe).
I have one each of the notched and smooth legs. Entirely personal preference here, I think. For action shooting, I would generally set the leg length at the start of the stage and leave it there, in which case the adjustment type doesn't matter much at all. Notched legs will make that task slightly more convenient.