I used to have some gaiters. They were miserably hot in the summer. My legs from the knees down would be covered in sweat, boots and socks looked like I spent all day in a creek. I can't imagine chaps would be any better and would probably be worse. I either never got struck, or if I did I never felt it. I would opt for boots if I did it again, and could find a comfortable pair.

The Wilderness Medic in me has the following, related, opinion:

What kind of snakes are you worried about and how serious of a threat is it? And how far away from care are you in the event of a bite?

Nobody wants to get snake bit any less than I do, but I've decided that the best defense is a good offense. Worst case scenario like that is I get a full venom strike from a copperheaded water rattler and I'm at a hospital in 35 minutes. The more probable worst case with gaiters or chaps is I lose too much water via sweating from my knees or thighs down, and have a heat related emergency. Thats actually a bigger concern to me. My advice will be different though if you're in the middle of a diamondback nesting zone.