MH VS HPS - Which puts out more heat?

Which puts out more heat? MH or HPS?

MH gives more heat... but, having either MH or HPS ballast you still can use conversion bulbs (MH > HPS or HPS > MH). The main thing is that both of them are ideal for growing, but MH is perfect for vegetative stage (for flowering is pretty good too) and HPS is perfect for flowering/budding stage.

So, in general, you can have any kind of ballast and use conversion bulb if you need to use different type of bulb.

Happy growing :)