I also have both. I think the Atlas is better equipped to handle "odd" shooting positions where you don't have a choice but to set up on uneven surfaces. It's also slower to set up and I find the knob used to tighten the swivel/cant to be finicky (either too tight or too loose). It's still a nice piece of kit, but the Harris is simple and sets up quickly. One of my Harris bipods has the DLOC setup from ZroDelta (I bought it back when they were Alamo Four Star) and I really like the ease of operation of that bipod. If you are mainly shooting off a bench, I would opt for the Harris.
The stock Harris bipods attach to the swivel stud. I have rails on all of my rifles, which is why I opted for the DLOC adapter version for the last Harris I bought. Both bipods are stable. You can buy knobs for the Harris that make it easier to remove, but it only takes a minute either way. With a quick release for the Atlas (the version that's around $280), it comes off with the flick of a lever. The base version requires an allen wrench to remove.