We have a ventless NG fireplace in our house. The first few years it was great - took the chill off the room in minutes flat and saved a ton on our winter fuel bills. This year, we simply can't use it. I don't know what the gas company has done to our gas supply, but the thing stinks up the whole house. It is not just our fireplace either. The oven, water heater, and downstairs ventless stove stink as well. Our friends in the neighborhood have noticed the same thing.
So I guess what I am saying is, I would go with vented gas if you want heat, or a pretty electric if you just want ambience. The stuff on the market now is very nice looking without the headache of a real fireplace.