Ittsuu vs sanshoku

Hand state, where viability of either yaku is available.

A choice given between two forms of sanshoku (123 or 234) and ittsuu.

Ittsuu and sanshoku doujun are similar but incompatible yaku, because hand does not have enough space for both yaku. When a hand has the potential to score one or the other, a player must choose which to aim for.

Formation

Ittsuu and sanshoku require 3 specific sequences. They are both worth 2 han closed, and 1 han open.

However, according to monthly data in Tenhou.net, sanshoku is around twice as frequent as ittsu. This is due to a few reasons:

• It is easier to make a 345 sequence than a 123 sequence. To make 345, a player can have {34, 35, 45} in hand. To make 123, a player can only have {12, 23} in hand.
• Players prefer middle tiles over terminals for tile efficiency reasons. This means they are more likely to have a 34 or 45 ryanmen than a 12 penchan or 23 ryanmen. Thus, it is easier to "incedentially" form sanshoku than it is

Also, sanshoku is compatible with tanyao and chanta/junchan, while ittsu is compatible with honitsu/chinitsu.