Put me down as another one where it depends on the quality. 10 times where she and/or I wind up unconsious -v- 20 that comes down to mutual masturbation and I’ll take the 10 every time. All else being equal? I can count.
Someone wants to blackmail me with pics of me with ten women at once? Hell! Send me the 8x10 glossies and I’ll frame em and hang em on the wall!
Woman here.
If it were a forced choice, I would choose the 20 times with one partner.
However, I would prefer to have 3 partners and with 3.33… times with each one. Three and a third times would be enough to get it right without getting too emotionally attached and heartbroken, and I would have the anticipation of the next two while I was with the first partner.
Okay, I can’t count. I’m going to change it to 6 partners 3.33… times.
Okay, since a few people have raised the age issue, maybe that makes a difference. I’m in my fifties and I chose 1 woman 20 times.
However, I can still remember my teen years and based upon those circumstances, I’d say … 1 woman 20 times. (Maybe even more so, if I were a teenager. Again the math - as a teenager, would I like to get laid 10 times or 20 times? hmmmm decisions, decisions … 
)
My first response was 1x20, but I think I’m going to have to change it.
10x1 is the kind of awesome fantasy situation that none of us, in real life, will ever see. 1x20, on the other hand, implies a relationship. There is not a woman in the world that I’d want to have sex with 20 times and then just stop. If I want her 20 times, I’ll want her hundreds of times.
If I have sex with one of the ten women more than once in a night, is that ok? IMHO, sex with somebody the first time generally leads to sex with the same person later that night. Although the OP states it’d only be once, I tend to use “once” to mean one night, not one… session, if you will. In that case, the numbers pretty much even out, after the 20th time you’re with a person, depending on the circumstances, of course, and again, IMHO, it’s less likely that one will be waking the other up at 3:30 in the morning for round two. Or three, or whatever the case may be.
I’ll take 10.
What are you, a goddam MACHINE?!? I’m getting tired just thinking about that.
Sillies! The answer to the OP, is, of course, “yes”. 
Like some of the others, I’m kind of in-between: 3 or 4 partners, enough times to get to know them.
I’m a little confused about the 10x1 scenario. Are we talking about 10 lovers in series, or in parallel?
I am assuming that what is being discussed is whether you would prefer to have sex with ten different people on ten different occasions or have sex with someone twenty times on twenty different occasions.
If this is the choice then I’m going to go with sex with ten different women over a period of time as opposed to sex with one woman over a period of time. Maybe there is something I’m missing here, but we don’t seem to be talking about all that long a relationship. Its not the love of your life, but rather that girl you dated for a while Sophomore year in college who never returned your second favorite T-shirt.
Now if the option is ten different women at once, than I would go for that. It would be worth it just for the experience alone.
Absolutely 10 different. I love the excitement of the first time.
In series, and probably not on the same night. That was (is) a misconception I’ve seen a couple times in the thread, probably due to a misread of the title as: Would you rather have sex with ten partners AT once, or one partner 20 times?
Baloney. Ten women one time each. Any man who says otherwise must immediately relinquish their membership card.
I’ll say ten partners once. Variety is great, and as Foxy said, always exciting. In my youth that was quite an unbeatable combination.
Jeez, either would probably get me a divorce.
Various answers:
Just kidding on most of those… except number 5. 
As long as it’s been since the last time I had sex with anyone but myself, I’d settle for 1 time with 1 woman at this point.
You’re getting tired thinking about sex twice in one day?
Even if both numbers were ten, I’d go with ten times with one partner. If it were once with twenty partners or ten times with one partner, I’d still go with the latter. I’m just not a one-night-stand kind of guy.
No, it’s a deliberate misconception, because it’s funner that way.
I guess that I didn’t answer the question seriously. My bad.
It’s an age and relationship issue. I’ve been there and did the 10 partners (actually a lot more than that) before, and I’m very monogamously married now so I get the 20 times now.
At the time I was hanging in bars, I preferred the multiple partners, because of the excitement, but then I wanted to settle down. My wife is better than all the rest, so I have no complaints about the situation at all.
As a straight male in a monagamous relationship, I’d probably have to say ten different partners, there have to be a few amazing ones in there somewhere. But safe sex and condoms suck.