I am interested in purchasing a stove top griddle. Does anyone have suggestions on what type and brand they prefer?

"Baking Steel" now offers a griddle as well as the steel baking 'stone.' I have an induction cooktop and am really pleased with it. I use it over two burners that are the same size, preheat it for a while, and the surface temp is relatively even and it came well-seasoned -- I tried the bagel version of toad-in-the-whole and the bagels and eggs released perfectly. At 25 pounds, it's seriously heavy, though, which could be a drawback for some. I just checked the current price -- I bought it at the pre-sale price (we have the baking steel and love it) -- at $199, it's also seriously expensive, but you will never, ever have to buy another stove-top griddle.

I've never cooked on a flat top so I can't answer that part of your question, but I have a cast iron Lodge brand griddle pan. I like it but honestly I usually just grab 2 cast iron skillets instead. I don't like how the center of the pan doesn't get as hot as the portions directly over the burners. Also there is a depressed strip along one of the long edges that I'm assuming is for crumbs, extra oil, or other food bits that might accumulate add you cook. I wish it wasn't there because I don't like cleaning it and I don't use it so it essentially just makes the surface narrower for me. The opposite side of my pan is a grill too which I've used only a few times because it is a project to clean.