How to choose vibration motor

There is 2 typical vibration motor:
1.cylindrical motor
2.coin or flat motor

How to choose a motor for a mobile.
Usually,cylindrical type vibration motor have strong vibration and customer choose cylindrical motor before.
But now customer like coin type vibration motor better.
Why,
1.vibration motor have strong vibration but also noisy.
2.vibration motor are not easy to assemble and high unquality rate as it assemble outside.
3.compare from motor work direction and the position of the center of gravity differ to different vibration.Pls refer to follow picture.

 with love