I’m going to say Clapton, but only because of Cream.
The Replacements or The Smiths?
The Replacements, because Morrissey sounds like a Muppet.
Van Morrison or Paolo Nutini?
Van Morrison, because I’ve been listening to his music since childhood and I barely know who Paolo Nutini is.
Bob Dylan or Tom Waits?
I love Cream and some of his other work, but you’re still dead to me. 
Dylan, but that’s close. Both have written timeless songs. But Dylan changed how songs are written.
Squeeze or XTC?
Squeeze. Not even close.
The Kinks or the Small Faces?
Kinks because of ‘You Really Got Me’ has my absolute favorite guitar solo.
CCR or The Band
CCR- Fogerty is a jerk, but a brilliant jerk!
KISS or Van Halen?
Van Halen, by a country light year. Kiss’ greatest talent was for selling merchandise.
Leonard Cohen or Lou Reed?
Eclectic power pop chiming in…
The Cars or Oingo Boingo?
Gotta go with the Cars here. I can still remember how fresh they sounded when they first came on the air. No one was doing exactly what they were doing at that exact moment, and I value originality.
Hmmmm… Credence Clearwater Revival? or Canned Heat?
Leonard Cohen for the music, Lou Reed for the influence. So… Cohen? I guess?
CCR easily over Canned Heat, not just because the vocals don’t sound like Kermit the Frog.
Blur or Oasis?
CCR. I know tons of CCR songs, all of them good. I know like one Canned Heat song, and I don’t really care for it.
To go in a different direction, do you like your electronic music mainstream and pop-y, or frenetic and weird:
Daft Punk or Aphex Twin?
Like both, but Oasis by far. I have owned most of their albums at times, while for Blur only their greatest Hits.
Oasis had by far the better songs, and had more success here in America. “Wonderwall” is a great 90’s songs, nothing Blur did was on that level, even album wise as “What’s The Story Morning Glory”?.
So Oasis wins.
I’ll let some one else take over the Daft Punk vs. Aphex Twin as it still stands.
Aphex Twins leave me cold, but I’ve always found a song or three to like from Daft Punk. Plus, that’s cool name points.
An obvious offering from me…
Alice Cooper vs. Ozzy Osbourne
Dang, that one’s hard. I’ll go with Ozzy.
Waylon or Willie?
Willie by a mile
Janis Joplin or Gracie Slick?
Willie can sing; he wins.
Grace Slick Who? Janis put her heart in it. She wins.
Fifth Dimension vs. The O’Jays
Fifth Dimension, if only because they have Marilyn McCoo.
Little Richard or Chuck Berry?
We’re over, man. Just over.
Out of Richard and Chuck I’d pick the litter. The former just seemed way too pervy for my taste and Mr. Berry still rocks my socks when I hear him.
Pink or Cher?