Plastic v. leather

I use both, but I find myself using plastic boots more because they're much more likely to keep your feet warm and dry. I climbed Rainier in leather boots and wished I had used my plastic boots instead -- but it wasn't a real problem.

If you're going to do Gannett someday leather boots are a better option because you can wear them on the approach, instead of carrying a huge pair of plastic boots for the mountain.

If you want to buy used climbing equipment, look for a store that sells used gear, that way you can inspect it, make sure the crampons fit with the boots, make sure the boots are in good condition, etc.