Individually? Far more powerful. For example, the British Grand Slam was one of the most powerful conventional bombs used during the war, had a ~6 ton blast yield (i.e. made a blast equivalent to 6 tons of TNT. Also, going from memory, I don't have the relevant sources in front of me at the moment). The Little Boy weapon dropped on Hiroshima had a ~15,000 ton blast yield (sources differ, as the weapon was never tested before it was used). I'll let you do the math, but that's many orders of magnitude greater.

Keep in mind that it can be a bit of an apples-oranges comparison. Different types of weapons have different effects. A high-explosive bomb does most of it's damage via pressure waves and mechanical energy. With a nuclear device, you have that mechanical blast yield, but then you also have intense heat, short-term radiation, and long-term radiation. And of course, if you're looking outside of 1:1 comparisons, it was thousands of "tiny" incendiary bombs that led to the deadliest air raids of the war, even before the atomic weapons were used. The difference lay in the effort needed for such destruction, but air raids were capable of killing of 100,000 people at a time without atomic weapons.