Well you'll have to ask yourself what you want to use your computer for. Also if mobility is a factor for you. For some, they'd want extreme power and don't mind being stationary. As for me, I like the freedom and my system's got enough power for all my needs. My rig's got enough power to handle any game at full settings- so I'm happy. I also take it to work, grandparent's house, friends house, girlfriends house... game where ever I feel like it... even the toilet.
As for heat, laptops and desktops will generate heat, fans will kick on to dispurse it. It's a normal thing, its just that the desktop isnt sitting infront of your face. For gaming hardware, the laptops are stuck at 7800 gpu's right now, but you'll be seeing more trickling its way out soon. ATI's x1600 is already out now also. But the major question is in the first section- do you need/want mobility? If not, then a desktop is better for you.