I am in the process of getting a bow and was looking for some incite. I asked a question earlier about feathers vs fletch and got various answers depending on if one shoots off of the shelf or a rest.
This is my question. What do most guys prefer a rest or the shelf or is it just preference...does it make a major difference in the performance of the arrow (i would assume so if that is more contact with the arrow)
It is preference. I prefer having the arrow as close to my hand as possible. This helps if I need to cant the bow. Some recurve shooters find that using an elevated rest may help with accuracy.
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"I do not Hunt animals to Kill them. I kill animals because I Hunt." Roger Rothhaar
It is pretty much personal preference, as Bob said.
I like the arrow flight and somewhat improved accuracy I get with an elevated rest - on recurves. Elevated rests aren't aesthetically pleasing on a longbow. The other side of the coin is elevated rests can break at the worst time, so shooting off the shelf is one less potential problem.
So, I do both. For shooting targets and keeping score, I use a rest. For hunting and generally goofing off with a bow, I shoot off the shelf.
Like the rest of the guys said, It is really a personal preference. The only thing is if you're going to shoot off of the shelf make sure it is radiused so you get reasonable clearance. Seal skin, and the traditional fred bear carpet and striker work well.
Shooting off of shelf or rest
The other side of the coin is elevated rests can break at the worst time, so shooting off the shelf is one less potential problem. 
