From the tile efficiency point of view, leaving enough shapes (taatsu) to make groups (mentsu) while preserving a 1-4p nobetan shape which may be useful later.
From the te-yaku point of view, I'd rather aim for ittsuu if possible, sanshoku is kinda far away.
From the player point of view, don't want to discard any of 'em souzu tiles to the guy to our right, especially when it's the dora suit and all.
Also, it's important not to push so hard in this hand as well, as it's not likely to be a winning hand with this shape at this point. Rather, I'd try to see if I can make it build some menzen strength or fold it if it doesn't come together. That's why there's no point in just dealing every 1 and 9 in your hand praying for a tan yao or pinfu tenpai just to fall magically into your hands, but rather aim for some yaku while maintaining a good shape.
As an example of this line of thinking, a natural discard order could be:
(You'll have to picture the 5s as red)
The shape becoming considerably better. One away from tenpai and also you can take the one away from ittsuu (full straight) at the time you draw something in the pinzu area.
On the other hand, keeping that
will bring tougher and more delicate decisions quite a few times, but it will end up making you tray too hard for this hand which is otherwise not worth of it. Especially once you draw
as you won't be able to go for tan yao anyway and you'll most likely have to reach to get a yaku.
to fixate on tan yao in the first place is not bad, but it would kinda imply you have to discard
and you get an overlapped 2do uke (redundant wait?) for 2-5p. If you plan on calling tiles to win the hand fast and with effort, it's okay to discard
and go for tan yao, but I don't think the hand is worth of it. At least until you have another dora in it.
Also, another disadvantage of fixating on tan yao is that if you call from the 57s shape, you'll be in a problem when you draw the dora. That, and the shape is still relatively bad.
For such reasons, and probably a few others, my choice is
and then see what happens.