Which generates more heat a wood or gas fireplace?

Well is the question the total amount of heat, or total USEFUL heat?

In general, a wood fire burns a bit hotter than gas- hence the wood fired Pizza ovens. Hoever, gas fireplaces usually have a heat exchanger that draws in room air, warms it, and returns it to the room. It has less air going up the chimney than a wood fireplace (a major point of heat loss)

The chimney of a wood fireplace may be more massive brick, which will hold heat after the fire burns out.