Straight up depends on what you want to use the final product for
If you are doin a track just to be creative and amuse yourself and others and have fun, sample from vinyl records/ cd's whatever, wherever ignoring copyright laws because no harm done in personal use.
now, on other hand if you want to make sample based beats but the legal kind that you can legally re distribute/ sell
or license thru a place like
http://www.pumpaudio.com/artists/go ahead and buy royalty free sample sets because you are basically paying a one time sample clearance fee to the company for use of a bulk set. but being royalty free after that you can re-distribute the beats/songs for sale or license or free whichever is your thing.
you can kinda switch back and forth between the two methods, doing it different depending on what the beat your making is intended for.
sampling vinyl or other songs is def more fun but also a little limiting in some avenues. If you want to sell mp3 beats online to hobby rappers/singers do it however the fQ!3! you want to do, like a deejay sellin/ handin out mixtapes to get gigs