I don't know about best, but I've been impressed to varying degrees by the following:
Barry White - The Best of Barry White (20th Century Masters Collection)
Blessid Union of Souls - Home
Boyz II Men - Throwback, Vol. 1
*Cantus - Deep River
*Cantus - Let Your Voice Be Heard
*Cowboy Junkies - One Soul Now
*Cowboy Junkies - 'Neath Your Covers, Pt. 1
*Cowboy Junkies - Trinity Session
Cyndi Lauper - Twelve Deadly Cyns
*Diana Krall - Live in Paris (although all of the albums are pretty well recorded)
Dixie Chicks - Fly
Dream Theater - Awake
*Eric Clapton - Unplugged
*Fleetwood Mac - Rumors
Garth Brooks - Sevens
Garth Brooks - Scarecrow
*Goo Goo Dolls - Dizzy Up the Girl
*Hanz Zimmer - The Gladiator Soundtrack
James Horner - The Titanic Soundtrack
Jane Monheit - Taking a Chance on Love
*Jesse Cook - Gravity
Jewel - Spirit
Josh Groban - Josh Groban (the quality of his Closer album is pretty good but not great)
LeAnn Rimes - This Woman
*Lee Ann Womack - There's More Where That Came From
Liquid Tension Experiment - Liquid Tension Experiment
Liquid Tension Experiment - Liquid Tension Experiment 2
Live - The Distance to Here
*Loreena McKennit - Book of Secrets
*Loreena McKennit - The Visit
Martina McBride - Greatest Hits
Marvin Gaye - The Best of Marvin Gaye, Vol. 2 (20th Century Masters Collection)
Michael Jackson - History
Natalie Merchant - Tigerlily
Norah Jones - Come Away With Me
Norah Jones - Feels Like Home
Phil Collins - Hits
*Pink Flyod - Dark Side of the Moon (Gold Disc)
*Pink Floyd - The Wall (Gold Disc)
Ray Charles - Genius Loves Company
Sade - The Best of Sade
*Sarah McLachlan - Mirrorball
Sublime - The Best of Sublime (20th Century Masters Collection)
The Nylons - Perfect Fit
The Tony Rich Project - Words
I've placed a * next to the very best recordings among these