As to your question of 'the best', that's subjective. If you intend to use the fireplace a few hours a day, then the ventless may not be too bad. Ventless are usually about 99.5% efficient but if they're used a lot, folks with respiratory ailments may have some problems. And if you don't have anything adding some type of humidity to the air, the dry air may cause respiratory problems in sensitive folks too.
As to our question of heating the upstairs, you need to look into 'how' the air will be moved. Just rising up the stairway may not be enough. If there's a circulating ceiling fan in the hall or room at the top of the stairs, that will help heat the upstairs. If there's a particular ROOM that you want to heat, well, you have 2 options. 1) put a fireplace in that room, or 2) put a fireplace BELOW the room, and install a ceiling/floor vent to the level above. The heat will rise to the ceiling below and flow through the vent to the room above. Just a thought.
Other than that, I haven't much to offer other than probably what a salesman might have to say. My best to ya and hope this helps.