Is it good to suck vagina?

Suck yes, Blow no: Never blow into the vagina with the labial lips closed as this can cause an air embolism (air in the veins which can travel to the heart and lungs causing death) and that would 'suck big time.'.

If you want: Whatever floats your boat. Just be gentle.

Cunnilingus: This sensation may be very stimulating to the female. Whether it is good or bad is not a judgement that I can make for the couple. However, diseases can be transmitted via oral sex.