Many of us have different ideas on who was Scar's queen, or if he even had a queen at all.

SARABI

Sarabi is one of the more popular choices in fanfictions, because she was the queen during Mufasa's reign. That's pretty much the only reason, so why should she be queen just because of that? Surely he wouldn't want his brother's queen to rule with him. Although it is a possibility, I highly doubt it.

SARAFINA

Sarafina is one of the less popular fanfiction queens. The reason some people use her is because I have seen versions of Mheetu as Scar and Sarafina's son. I doubt this as much as Sarabi because this is the only reason, and not everyone follows that fan-fiction, but she was never Mufasa's queen, so Scar could possibly choose her.

ZIRA

Zira is probably the most used queen for Scar, because of Zira's love for Scar. I know a lot of you are probably thinking "Scar never showed any love for Zira, she was just a fan-girl!" well how do you know? The only reason he didn't show love for Zira in the move is because Zira didn't EXIST in the TLK universe, she wasn't a character yet, and Scar wasn't in the second movie (apart from the reflection and dream sequence) so the two never really met in the movies. Zira being in love with him and the fact that Kovu was originally going to be his son before they made him Kiara's love interest is enough to show the two more than likely loved each other.

NALA

Right now you are thinking "What NALA ewwwww that’s so wrong!" well I wasn't the one that though of that! This is actually the most likely queen. Not I didn't say fanqueen, because it is actually official Scar chose Nala as a queen. It is a deleted scene that was deleted because the creators thought it was too creepy and also due to time. It is also a scene in the Broadway musical of The Lion King (Madness of King Scar). Another thing, Scars first option is Nala, so either Scar actually didn't love Zira, or they met after Nala left.

Here is some info:

http://lionking.wikia.com/wiki/Original_Concepts_and_Documentations#Scar_lusts_over_Nala

http://www.youtube.com/watch?v=I0WATOVmLtQ&feature=player_embedded
 

NO QUEEN

This is just as likely as my Nala theory. Nala leaves for help after Scar chooses the Madness of King Scar scene, so depending on how long it took her to find Simba, Scar may have had no queen at all. If it took Nala a few weeks or a few months, then maybe Scar did have a queen, but if it only took a few days or weeks, then he wouldn't have had one, or had one for long.
 

CONCLUSION

4. Sarafina-I highly doubt her as Scar's queen
3. Sarabi-Higher than Sarafina, but still unlikely
2. Zira-Possible, if she was queen, not for long
1. Nala/No queen/Queen, but not for long-It really depends on how long is took Nala to find help, she wouldn't have found it straight away, so I'd say that Nala was the most possible choice to be future queen with Scar, and after she left, he chose another who wasn't queen for that long, possibly Zira (they obviously knew each other before his death)