Depends.
Are you picky about your audio quality? Can you tell the difference between a raw wave file and a 128Kbps sampled MP3?
If not, go with whatever gets you the tracks you want the cheapest. Amazon, itunes, whatever. They're all easy to use, itunes is DRM free now. It really doesn't matter.
If you are an audiophile that can't live without the absolute best quality digital file, you'll have to do more research.
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'He who receives an idea from me, receives instruction himself without lessening mine; as he who lights his taper at mine, receives light without darkening me.'
-TJ
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