We built our home and opted for a gas fireplace. I had a wood burning one growing up.
When I was growing up, we lost power in our house for 10 days during the winter. At night, we would sleep in the living room with the fireplace burning and my dad would wake up every hour or so to add more wood from the garage. It was a huge pain and if we had a gas fireplace during that time, it would have stayed lit and warm consistently. We have lost power during the winter in my current house with a gas fireplace and as a PP mentions, it did a great job of keeping the family room area around 60-62 degrees until the power came back on.
As mentioned, the wood burning fireplace creates mess, clean-up, and smell. The ambiance and smell is worth it to some people, but not to us. We knew it would stop us from using it as often as we would want to if we went with a wood burning one. I also recall issues with critters in the chimney growing up and eventually my parents stopped using it all together.
With gas, it can be more expensive since it will impact your gas bill and also has parts that may need to be replaced. We have had minor issues with the igniter.
One tip I have is to make sure your thermostat is far away from whichever fireplace you decide on. Ours is in the same room and the room gets so warm, that the heat will not click on and then our upstairs becomes cold. Wouldn't be a problem if you have dual zone though. If you go with gas, make sure the fireplace has the option to switch on the flame only without the blower to throw the heat. For us, the fireplace often makes it too warm in the room so we have to turn it off. We wish we could leave just the flame on for effect and ambiance, but don't have that option.