Well, we're first with almost 20k points lead and it's East 4 on an East-only game, so I'll just go for the fastest win.

seems to be the "least" interesting part of the hand, and since two

are already gone there are big chances someone will discard

for us to pon, especially if we discard a (third)

.
Then, I remembered we actually need a yaku, so I'll discard

and go for tanyao, keeping sanshoku 345 as a bonus or escape plan (in case we draw a

).
I may open the hand if the sanshoku goes further or if the 9m thread is cleared off.