I have prefer the wet carpet cleaning.
Wet - I have the Bissell Pro Heat 2X. I use Genesis 950 in it when I clean because it pulls everything out of the carpet and does not leave soap in the carpet. I also rinse with my machine after I have cleaned. When I am finished, I use a dehumidifier to help speed up the drying process.
I recently tried a dry carpet cleaning. I ended up with more mess than ever! I used this really tough powder, it had to be sat on the carpet for an hour, then when the time is right I needed to remove with a vacuum cleaner. I ended up vacuuming for over 2 hours, that stuff was everywhere! (Imagine big white grains of sand all over you carpet). I decided to leave the carpet cleaning to the professionals.