Secure way to do a sudo on linux server

Summary: We have a need to limit a linux user's ablilty to Sudo to specific other users

 We have 2 options for the Entry on /etc/suoders.d.

 

Which among these you recommend.

 Option A:

Cmnd_Alias SU=/bin/su - oracle, /bin/su - grid

username  ALL=PASSWD:SU

 this allows sudo su - oracle and sudo su - grid

Option B:

username ALL=(oracle,grid) ALL

this allows sudo -i -u oracle and sudo -i -u grid

For both the options, it doesn't allow sudo to root which is expected in our case. Now, we want to which option is more secure and recommended one from Linux Security point of view?