Larry said in an interview that Holly Harwood was his favorite mistress/affair.
In an interview with TV Guide in 1991 (around the time of Dallas' final episode), Larry Hagman said that Mandy Winger (Deborah Shelton) was his favorite mistress.
He also said in the same interview his least favorite mistress was played by an actress who smoked cigars without naming the actress/character. I believe he was referring to either Leslie Stewart (Susan Flannery), Angelica Nero (Barbara Carrera) or Carmen Esperanza (Barbara Luna).

Larry said in an interview that Holly Harwood was his favorite mistress/affair.

1. Serena
2. Julie
3. Sly
   If you're talking about FUN, these women seemed to do the trick for J.R. He was always laughing and being carefree in bed with these three women. The others seemed to give him massive headaches.
   Actors are useless without the power of a good writer's imagination

5. Afton Cooper - Something about being with a rival's girl. From the young chick to the old chick to another young chick. It must be great to be JR!
   Afton wasn't J.R.'s rival's girl when he bed her. Afton was his niece's future sister-in-law. J.R. bed Afton first, then goaded her into seducing Cliff to get his secrets. When Afton fell for Cliff for real, she dumped J.R.

Trick question!
You can't limit it to just three!
But my guess(es)

1. Sue Ellen - always a good guess
2. Holly Harwood - Must be something about that kinda power when a woman would go through you to get to your brother.
   I liked it when JR told her that she was new to the oil business and didn't know how things worked and urged her to sign a contract by saying "Now, scribble your name on that piece of paper and go outside and play." I think he stopped seeing her at about the same time.
3. Kristin Shepard - Must be something to be with the younger sister of your wife (especially before she finds out).
   Honorable mentions
4. Marilee Stone - Something about an "old chick," even though she wasn't THAT old, who (probably) doesn't have the hang-ups that younger chicks may/can/do. They've been around. They know the drill and if they want to keep seeing you, they'll make sure you want to come back. JR could "have his way" with her in the board room and the bedroom.
5. Afton Cooper - Something about being with a rival's girl. From the young chick to the old chick to another young chick. It must be great to be JR!

My guesses would be Kimberly Cryder, Katherine Wentworth, and Callie, or maybe that's just me!

I think Katherine and Kristin simply because they were sadity. Next would be his first Secretary Julie.

Buna, this sounded like fun, hana

1. Kristen
2. Marilee Stone… he seemed to keep going back to have a sniff!?
3. Rose McKay
   He only bunked Rosed McKay to make Carlton feel pain, hana

I made my list before I checked other lists. Marilee Stone made my (honorable mention) list, too!
While she was not THAT old, she was older than the average JR counterpart.
According to her unofficial IMDB bio, she'll be 70, in real life, in 2017, meaning that she was 40-something then? Not sure how old her character was supposed to be.

Marilee Stone he seemed to keep going back to have a sniff!?
What do you mean by "a sniff"? LOL
And LOL at Rose McKay.

1. Kristen
2. Marilee Stone he seemed to keep going back to have a sniff!?
3. Rose McKay

Julie Grey?
I'm sure that he'd prefer Mary Ann But that's different argument for a different show.
LOL. Or maybe he'd prefer Mrs. Howell. Or even Gilligan, not that there's anything wrong with that.

Julie Grey?
I'm sure that he'd prefer Mary Ann But that's different argument for a different show.

It has little to do with how good looking someone thinks someone else is although while she is obviously attractive I always found Mandy very overrated. I guess it has to do with the actual actors involved. Larry and Debra didn't have the on screen chemistry that he had with Linda Gray for example. I always thought Mandy was just someone for JR to have on his arm. When they have love scenes together, her moaning seemed fake and while he lusted after her there was something missing. Some kind of spark. It just seemed bit contrived. Just my opinion of course.

I would make Sue Ellen 2nd and Kristin 3rd. Angelica never existed in the show, so I am going to give her the axe.
You really think the JR and Mandy love scenes were forced? It seemed as if J.R. couldn't control himself when he was with her. He would be out of control when he would kiss/make love to her. I think it had more to do with how Mandy's pure beauty/sexiness aroused J.R. so much.

Personally I didn't think there was any chemistry between Mandy and JR. Their love scenes always seemed forced to me.
I am having to think hard here because he had so many. LOL
Sue Ellen has to be in there. The sexual chemistry (when they were good together) was great.
Serena- The call girl that JR spent many a night with.
Julie Gray- The secretary from the early days.
I also think JR and April had quite good chemistry. Much more than Bobby and April.
I think the woman he had the least fun with was Vanessa. I never got that one at all.