So the options are 2 Pin, 4pin, or 4 sou, 9-sou.

Both have similar effects Drop drop the 2 or 4p you have to wait on 5-8M and 4 and 9S. in total is 12 Tiles but over two third result in a tenpai with 4 tiles for wins but two different. In this option you drop the 2 pin if you draw the 5P you can work with that and change up from there.

4and9S is your 1 shanten tenpai option are 3P and 5-8M.12 tiles to reach tenpai with a potential out of only four tiles, However if you get the 3 Pin you can get Pinfu which would be nice. but is more likely to get 5-8M have wait on 3Pbut you advanve it better with a 5Pin draw and 3-6P wait for tenpai. I will go with go with cutting the 9 sou since it is a Terminal it maybe safe to riichi with later.

We're between pairs here, either 9s or 4s. There are equally distant chances of either 234 or 789 sanshoku here if four more necessary tiles come in. I'm not exactly expecting this to come in-- the standard pinfu form is much more likely-- but I want to leave the possibility open.

I can cut 9s hoping for 789 sanshoku with 4s as pair, or I can cut 4s hoping for 234 sanshoku with 9s as pair.

Not knowing the table situation I would throw out 9s here. 4s is too potentially useful to me and to the other players. Throwing it out-- especially if I throw two out-- looks conspicuous to the other players and could be dangerous.

Pure Efficiency:

9S, as the only improvement to that is 8S or 7S (8 tiles total), which is considerably worse than 4S pair's improvement (include 2S, 3S, 5S and 6S. 24 tiles total).