
We have post by G Uzaku san from Japan.
His MJ Books are the one of the best selling MJ tactics book, and especially regards "Tile Efficiency" related topics.
What would you discard and WHY?

Who is G Uzaku?
Mahjong books author. And he is also works for other Mahjong tactics books as Proofreading.
He prefer play real mahjong rather than internet Mahjong games.

『麻雀 傑作「何切る」300 選』
300 Selected WWYD (Blue)
『麻雀定石「何切る」301選』
Mahjong established tactic 301 selected WWYD (RED)

Newest one recently released
『ウザク式麻雀学習 牌効率』
Uzaku Style MJ Studies "Tile Efficiency"
(GREEN)
Picked Tile efficiency related subjects from Blue and Red version and adding more.
Highly recommended for players who just started and not winning hands often.
G Uzaku also running his blog
(Slashing MJ Books! Slashing MJ games!)
Twitter: @mjbook
Hoping for a pinfu shape, we don't need two pairs, so let's discard from one of those. It's a distant hope at this point, but this hand could turn into a 234 sanshoku if the right tiles came. Therefore, I'd discard 2s to leave that possibility open while still progressing the hand.
Afterwards, if I drew 3p it's time to forget about sanshoku and reach. On the other hand, if I draw 3s or 4s, I'll get rid of the 67m group and aim for sanshoku.
Dave, you have really good detailed reasons!! Thank you for posting comment!!
start with 2p. 4p, 67m, 2s8s can all be connected to. I won't take less than 2 han and a good wait in the end. 789/678 sanshoku is also still possible, but the final wait shape is more important so I will discard 2p first and see where I can find better shapes...
For Pure efficiency:
Go with 2S/8S, as discard any of them still allow this hand to have 48-52 possible tiles to improve (since singular tile is always worse on speed than a waiting shape)
For Maxium worth hand:
Go with 2P, 4P or 9P, as if someone may desire a 3 color straight of 678 and all-simples.