I am a '70's Motown guy... Stevie's stuff early to mid '70's but the very best ever on Motown... Marvin Gaye's golden quad... "What's Going On", "Let's Get it On", the underrated "I Want You" and the almost forgotten, but brilliant (though angry, which I happen to like) double LP, "Here My Dear".
Not Motown, but give me Al Green or give me death... "I'm Still in Love With You", the greatest "love/gettin' DOWN" record ever... yes, infinitely better than all of Barry White's music combined (see also Marvin's "I Want You" above... you're wife will thank me later).
The most underrated, though, after James Brown (one of the ten most important artists in the history of recorded American music)... late '60's to mid '70's Isley Brothers... don't sleep on the band that could play ANY kind of R&B you could name, the proof being that they did just that.
JMO, but I am right. Take it to the bank.