To answer the question, I have an oiless that I take to the job that powers my trim nailers and will run my framing gun for light framing. I have also used it for roofing with no problems. To get something useful in a lug around compressor you will need to get something that will kick out at least 2.5 CFM at 90 lbs. And of course, MORE is always better depending on your needs.
Oiled compressors are generally quieter than oiless, and both of my oiled pull an amp less than than the oiless. In this case I believe the amp rating because my oiled compressors never blow a circuit, and the oiless frequently do. Taking the oiled out to a job where the breakers frequently blow seems to solve the problem.
For me, I actually prefer the oiless since there is no maintenance to keep up with, and no oil to leak out when it has ridden around in the back of the truck and been banged around on the job for a while.
Lots of talk about oiled compressors lasting longer than oiless, but in actual everyday use for me that hasn't necessarily been the case. I haven't actually had the pump itself fail on any of the last several compressors I have owned, it is always something else that gives up, breaks, or wears out. If it is a shop compressor, made for you to goof around with on the weekends and evenings on projects and then maybe some light remodeling, I would probably go with the best deal dollarwise. Sears has some good sales on occasion on compressors that have the same pump assembly as some of the Bostitch, Senco, and Porter Cable compressors (made in Taiwan or Itay).
If you don't have your nail guns yet, there are some great combo deals floating around out there.
Robert