I have a combination of old and new cast iron - both work well for me. I also still use non-stick for certain applications.
Generally speaking, older cast iron is better simply because the manufacturing process on older stuff included a better finish, and you often have years of use on it that (if cared for properly) has a good seasoning already. But old doesn't automatically mean better either - and you have to be wary of used cast iron because often it was relegated to "other" uses when stainless and non-stick took over and cast iron became secondary.
For example - I've seen several old cast iron cornbread and muffin pans that were used to cast lead ingots. Not ideal to return back to cooking food on. I've seen several that were used for oil pans and that have spent years in barn or other environments that would give me serious pause as to returning them to use for food.
Lodge is the most common modern brand, and they make good stuff. The issue with the newer stuff is lack of a mill finish on the surface, which means it is a rougher surface. If you are halfway handy, it's easy and not time consuming to take a sander and smooth a rough cooking surface out and then re-season.
Older cast iron includes Griswold, Wagner and MSR brands. All made good stuff that if in decent shape now can easily be brought back to life and used well.
No matter what - clean your damned cast iron. Old carbon and grease crusted on the surface is not seasoning, that's piss poor hygene. Modern soaps don't strip seasoning like old fashioned caustic lye rendered in the back yard did 100 years ago, so don't buy into the idiotic mentality that you don't wash or clean cast iron.