Sorted from least to most preferred
Azusa- Has the least knowledge about Ricchan. would most likely rather have the club practice, would be unreliable as a wingman if she tried being the youngest.
Yui- Wildcard. Enthusiastic to a wingman, but would not be very subtle about it. She's either going to be a fantastic wingman, or you'll be spending most of the time trying to cover for her mistakes, all in a short period of time.
Mugi- The most enthusiastic. Also has access to resources such as movie tickets, theme park tickets that can be used to drive you and Ricchan closer.
Mio- By far the most knowledgeable about Ricchan, but you have to prove you are worthy first. She can convince Ritsu to go places or do things that can help you two get closer, like no one else in the club.