Ittsuu vs sanshoku

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.

Hand state, where viability of either yaku is available.

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

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.