This may sound a little weird, but my favorite Mac(s) are the Mac(s) that were never released, that we have never seen, that have gone unknown to anyone accept those who created it.
Why are these my favorite Macs, you might ask? These are the design that provide insight, to the successes and flaws towards the final design. Jobs, Ives, and company learn from this, to bring us the best design possible.
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However, to answer the question as the OP intended, my favorite Macs was the Black MacBook. Not only did it look sexy, but the hard drive, RAM, and battery were all easily user serviceable.