I lean towards all metal models, I like most of the old straight stitchers, but I haven only had my hands on the most common.
I like the cast iron straight stitchers, there is a couple of them that's very nice.
I try do avoid the late 60s, 70s and 80 models with the worst reputation. If you want stretchy stitches there is hardly a model out there with out plastic gears. Some of my favorite zigzaggers have a few plastic gears like Bernina and Elna. They are nice to work and capable machines. That's why I have a hard time rouling out types of machines generally. If I find something interesting about a machine, or think it might be a good regardless of it's reputation I will take it on. There is a limit to much time and money I will spend on a machine, but with a good one I will go the extra steps. Less so with a very plasticy model.
An example is the Touch and Sew, they have a few fancy features some like a lot, others again find them cumbersome. There some solid all metal models among them, some were better than others. Hard to disregard them totally.