The true oldies station, playing AM/FM hits from the ’60s and ’70s with an emphasis on Motown, is "KOOL" KQLL at 102.3 FM/1280 AM. We'd say this is the "best" (i.e., the most traditional) oldies station.
Another good one, however, is KNYE 95.1 FM, which plays some tunes you've heard only a 1,000 times, not 100,000.
A somewhat new format (over the past 20 or so years) is known as "rhythmic" or "jammin' oldies," with playlists from the 1960s through the mid-2000s emphasizing disco and dance genres. On KOAS, 105.7 FM, you'll hear everything from the Four Tops, James Brown, and Mariah Carey to Curtis Mayfield, Janet Jackson, and Rick James.
There are also a couple of classic-rock stations (music ranging from the late ’60s to the late ’80s, focusing on commercially successful hard rock). KXPT at 97.1, also known as The Point, advertises itself as "Number One for Classic Rock." KKLZ at 96.3 plays similar music, though the rock is perhaps a little harder, from the ’70s and ’80s.
A couple other stations with oldies or classic-rock formats are KLUK at 97.9 FM, also known as Lucky 98, and KRRK at 101.1, or K-Rock. Both of these are broadcast out of the Laughlin-Kingman-Lake Havasu area and can sometimes be heard in or near Las Vegas.