IMO, go direct vent. The top vent (regular chimney) is just that, a regular chimney pipe - a single pipe carrying combustion products out of the home. When using a regular chimney, the combustion air comes from somewhere else, usually leaky windows, doors, bathroom fans etc. To me that means you lose comfort (it's drafty) in those areas where you're pulling combustion air into the home. And the pipe gets hot so you have to respect the proper firecode installation rules. On the other hand, direct vent chimneys are double-wall pipe. The center pipe carries the hot combustion products out of the home and the surrounding outer pipe brings in the outside air. That cuts down on the drafts at doors and windows, plus the outside of the vent pipe runs cooler, so it should be safer from a fire standpoint (you still install it per the firecode). The safety of direct vent IMO would be higher. I don't think there would be any major difference between installation, cost, appearance of the fireplace, or flexibility between the two options.

Tagging along...we are having two new gas DV fireplaces installed in our home renovation. We just got the plans for final bidding and the architect spec'd out the "Majestic khldv600 Marquis." It looks nice but it is very expensive. He seems to have strong opinions based on his past project experiences so when he specifically specs something out it typically means he likes it a lot. I'm interested to hear other people's thoughts on brands, features, and quality.

Not sure if you're still looking, but I wonder if the Heat'n'Glo Slimline Fusion would work for you. I am also looking for modern gas fireplaces and got information on this one yesterday. It has a linear flame, a modern look and puts out 12,000-17,000 BTUs. (There are other versions of the Slimline, so be sure to add Fusion if you look it up)

Find a gas fitter who installs fireplaces and have them uninstall and re-install the fireplace properly.