The important thing is that the insert you select be a direct vent system. They are the safest, most energy efficient. If your choce is between 2 direct vent systems, select the one you think looks nicer. (I assume your dealer turned them on so you could see how they look when lit.) You might also check the BTU ratings, which tell you how much heat these systems put out.

Be aware that these systems are a big job to install. It takes one or two guys at least 4-5 hours to complete the job. A special chimney cap needs to be put in. It's important that your installer check out your fireplace before comitting to an installation -- to take measurements, the location of the gas line, etc. Ask around to make sure your dealer has experience in putting these things in. You don't want to be on the low end of his learning curve. Another thing: make sure you get a remote thermostat, because these units can get real hot, like a blast furnace. You'll be turning it on and off pretty often unless you have a thermostat.

When we did a major renovation, we installed a Napoleon gas insert in the [former] woodburning fireplace in the master bedroom on the second floor. We couldn't see hauling wood upstairs and ashes downstairs, so went with a gas insert. While considering the efficiency of the insert, also consider the heat output and the ability to vary the heat output. The range of BTUs may be a factor, with more variable being better, to adjust to your comfort level. Ours can go from 25% to 100% which serves us well where we can see temperatures of -40 degrees in the winter (run it on high) as compared to late fall (run it on low).