I have an LG 1080p 60" plasma that I picked up a few years ago for $1200, it's a good TV, I don't feel as though I need 4K because it still hasn't become mainstream and few services actually offer 4K video. I think it will be a good 5 years before it starts getting big enough to justify.
Word of advice from me
Don't get a plasma, you'll never see your meter run faster.
If you plan on getting a 4K tv and there is nothing wrong with your current TV, you might wait, prices will drop between now and when it goes mainstream.
If you don't have a sound system, get a soundbar that is the same brand as your TV unless you are going for surround sound.
Ensure you have enough HDMI, DVI, VGA, A/V, whatever ports to cover the devices you will be hooking up.
Look at LED TVs, they are typically the lowest cost on your electric and have great picture quality.
Get as big as you can afford (or fit in your room)
Samsung typically has the best display, and the best looking TVs.
Sharp typically is right behind Samsung.
Be wary of Vizio and other Walmart-brand names, they may be cheap, but not your best bet.
I plan to buy another TV in a couple of years, I plan to get a Samsung 70" 4K, I'll make sure I can hook up an Xbox One, a Wii U, and an Apple TV (3 hdmi) I'll probably look at 4 hdmi ports just as redundancy or if I get another device to hook up to it. I'll also make sure it has no less than 120hz refresh rate.This is me, if you want to base a decision off of it, go ahead.
Nothing will help you decide better than actually looking at and listening to the TVs, except maybe the dent on your wallet.