Not all two-sided waits were created equal. Keep this in mind when trying to decide which wait to cut.
Let’s make the assumption that you only need a fast hand and no additional value and that there are no conditions in the discard pools you need to worry about. (If only mahjong were ever this easy!)
You choice is cutting either the 6p or the 3m.
This is where you need to have developed some vision about your ideal end wait. 1 and 9 suit tiles are the most likely to be thrown by other players due to their inflexibility. Followed by 2 and 8 etc. etc.
So your ideal wait location is the 23m. Thus, you throw the 3m to lock that in.
(If you draw the 6p and don’t want a riichi only, throw the 1p and stay 1-away on a tempai.)