There are many factors to consider when trying to determine which fireplace will put out the most heat. The type of fuel you use, the efficiency of the fireplace, and the size of the fire all play a role in how much heat your fireplace produces.
Wood-burning fireplaces are typically the most efficient when it comes to heat output. That being said, there are many different types of wood-burning fireplaces, so it is important to choose one that is designed for high efficiency. Gas fireplaces can also be very efficient, but they vary widely in terms of their BTU output. The size of the fire also plays a role in how much heat is produced - larger fires will produce more heat than smaller ones.
In general, though, if you're looking for a fireplace that puts out a lot of heat, a wood-burning model is likely your best bet.