More BTUs naturally means more heating power. But how many BTUs you actually need depends on both the size of your burner and the type of gas used.
A burner up to 20 inches in diameter should offer enough warmth to an area with 40,000 BTUs or more. Many of the portable gas fire pits use up to 60,000 BTU for a powerful heat. Any less than 40,000 BTUs mean you are basically investing in something more for decoration than heating purposes.