Both have there pros and cons but I prefer to use laptop as it is more convenient as compare to desktop. It is compact in size, takes very less space and has very few wire (just one power cord to charge it) system. It is light in weight as compared to desktop. Due to its portability and mobility, it can be used anywhere, anytime which is a great feature.
I use only Desk top. I have two desk tops to use- one at residence and another at office. Some times, I also use desktop in cyber cafe. Desk top is more convenient if you work from fixed point and do not have to move places.
Both desktop and laptop has their own advantages. If you are a person who travels a lot then laptop will be the best option. Whereas desktop will be the perfect option for people who stay most of the time at home. Space is the another factor that should be kept in mind while deciding whether desktop or laptop. For instance if you are cramped for space, then laptop will serve you best otherwise desktop is the best option. Performance wise desktop is better than laptop though.