I spent a lot of time looking into ballheads and reading various reviews before opting for the Markins which I have to say is awesome.
I was a little put off by the elliptical ball on the Arca swiss being prone to locking up.
I liked the simplicity, cost and weight of the Markins.
I have been using mine in the field now for some time and it has never missed a beat. It has a brilliant system for quickly setting the sweet spot on a camera lens combo and then locking it in on a small dial so you can turn the main knob to unlock / lock very quickly.
I have no experience of RRS but they certainly look well engineered
I would certainly look into Markins there is a youtube clip of a Nikon 800mm lens and camera being used with one.
I have to say mine locks absolutely solid when you tighten the main knob with the ball in any position.
There are different weight rated ones to suit most cameras & lens.
They even do a titanium one
I ordered mine from light n space on ebay from Korea as it worked out cheaper than buying from europe even with import duty. (I didn't have to pay any anyway as it happens)
My Arca-Swiss Z1 doesn't lock up, ever, with massive loads on it, at any angle. And, it doesn't slip either. I've had 25+ lbs hanging off of it and it is smooth as butter. Now, for the users who have the drag set wrong, or try setting it too far when the lock knob is cranked, that is where it's known to freeze up. But, you aren't supposed to screw with it like that.
I think the people who have problems with that are like the Hasselblad owners who complain about the camera locking up and that Hasselblad's are "junk" - usually caused by out of maintenance/damaged/neglected gear and/or really lacking in skill (not knowing how to use the camera). In all the years and all the Hasselblads I've had, never had one lock up. Some enterprising third-party even sold a tool for recocking the camera - never known anybody to own one, though.
When I had Manfrotto ballheads, they slipped like somebody had greased them with bearing grease, even a 70-200/2.8 could make them move on their own - straight junk.
The Markins are pretty much a knock-off of the AS heads - had a Q20 for a short while. It didn't like the cold and had some big issues with the drag not working, so I went to the real thing and the Z1 is great, even in -10 with blowing snow and high wind.