Source: http://blog.jpmahjong.net/read.php/621.htm
Hands with a difference of 2 han
Discarding 7 sou here will not give you pinfu and there's a 2 han difference between the good shape and the bad shape.
In this kind of situation, the key here is the amount of dora that you have.
You have no dora
The riichi with the good shape is only worth 1300 points, whereas the riichi with the bad shape is four times of that, therefore it is better. Without any dora, declaring riichi with the bad shape is the basics.
You have one dora(or there are other yaku worth 1 han, like tanyao)
A damaten with a bad shape(5200), riichi with a good shape(2600) and riichi with a bad shape(8000) are all possible choices. To make a decision, you'll have to look at the points situation here.
In a situation where the points are even, most people will declare riichi with a good shape. Even though damaten is worth twice that of riichi, but if you factor in ura-dora and various other advantages, I feel that riichi is a better choice, especially when you're waiting for number tiles like 3 and 7.
If you're after security, or if you're in the lead, you can choose to stay in damaten. This will give you the possibility of going into betaori.
If it's close to the end of the game and you need tsumo haneman for gyakuten, declaring riichi with a bad shape can be a possible solution.
You have two dora
Normally, the condition should be the same as that of dora 1. In a situation where the points are even, declaring riichi with a good shape is superior to declaring riichi with a bad shape.You have three dora
If riichi and damaten are both worth mangan, declaring riichi with a good shape is obviously better.
