We've recently been using harness that's made out of a woven cloth, that goes around the belly behind the front legs and around the neck in front of the legs. Most places here stock them for small dogs, and you have to work to find one small enough for some cats, but the cat/dog kinds are pretty much interchangeable. The cats seem to be fairly comfortable with them; but there's no kind of restraint that a cat can't get out of if the cat gets scared or is determined.
The place where you take the cat, and avoiding anything that might scare them, has more to do with it than what kind of collar/harness you use. Getting them familiar with the leash, in familiar surroundings, is a good idea before venturing into strange circumstances; but with most "domesticated" cats it shouldn't take much training.
I had to "walk the cats" on leashes on the army post (lots of coyotes in the Arizona Desert so housing rules prohibited "outdoor pets" unless on a leash.) The two we had then were reasonably acclimated to a leash, so a simple neck collar was sufficient. We later lost one who pulled out of a "full body straight jacket with chains and padlocks" when HE decided he didn't want to walk with me, and ran off and hid. He's only been gone about three years, and he's "chipped," but we assume he's killed all the local livestock and moved on to greener pastures (he was at 27 pounds when he got loose).
We recently lived in a camper (total living space 8 ft x 11 ft) with three cats, for three months, and walked those a few times with no difficulties; but we were careful to do it only when the crowds were minimal and the campground was quiet.
A rule to know with cats - just in case one gets rambunctious - is that regardless of how they're hooked up, if they get their ass away from you they can back out of any way you've got them tied on, so run around to the other end if you want to keep them tied on.
It varies with the cat; but few of them have any real difficulty accepting a leash if you work with them a little.