There's basically three types of flatscreens: LCD, LED, and Plasma. And in general, that's the order of their pricing as well, in increasing order. LCD is generally being phased out in favor of LED, which is actually a type of LCD that provides a better quality picture. Plasma does provide the best picture, but there are drawbacks beyond price. Namely, unless you view primarily in a darkened environment, there will be glare from reflections on the shiny screen.
I'll second the Vizio recommendation from gmart. Hard to beat on a price vs. quality comparison. And for the money, I recommend LED.
As for smart tvs, I've never used one so I don't know. But my feeling on that has always been that it's not worth it, as it's easy enough to hook your full-up computer or laptop (or web-enabled gaming system) to your tv for free, making it a hell of a lot smarter than a "smart" tv.