Does your home have a heat pump? If so, your house heat pump is 3 to 4 times more efficient than the waste heat produced by your computer, and you are using 3 to 4 times more electricity compared to the same heat output from a heat pump.
Of course, energy has to be expended to move heat around, and there are inefficiencies. But with real-world equipment and common cold-but-not-too-cold temperatures, a single unit of electricity can be used to move several times as much heat as it would produce if you just converted it to heat directly.
A computer is as efficient as anything when it comes to converting electricity to heat. Heat pumps win because they're ultimately playing a different game.
But, thanks for clarifying.