I'm not sure what you mean by "conventional", certainly a plain resistive heater drawing 500W emits the same amount of energy as a computer drawing 500W. If you stretch the definition of efficiency, an infrared heater produces a similar subjective improvement to a room's temperature for less energy, as the infrared light skips heating the surrounding air and warms the subject directly. That is one downside to using computers as heaters - they produce almost no infrared, which can be less efficient for a given subjective experience.
I use a resistive heater. A heat pump would be about 1000 times noisier, and I live in an apartment, so I couldn't put the heat pump where I don't have to hear it.
I have both a heat pump and resistive heating in my house. The compressor goes outside the house so you never hear it (and it's not particularly loud, just sounds like a quiet powerful fan). The indoor split units, as they're called, just blow air over the coils. The fans are very quiet, quieter than a typical standing fan or an A/C vent blowing air.
Resistive heating is usually much quieter, however it can make annoying ticking sounds as the metal expands against the wall, or an annoying electrical buzz as the power is cycled on and off, multiple times a minute. This happens even if they're installed perfectly, houses and walls move over time.
