What's the difference between XBox 360 Arcade, XBox 360 Elite, XBox 360 Pro?

My 10 year old son wants to get a used one off of craigslist but I have no idea what the differences are between the units.

♦Which XBox 360 is the best?
♦Which ones are more likely to get the RROD's (red rings of death)?

Let me know your thoughts. Thanks for your help.
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