If he/she is full
If your baby has a strong suck, can take 2-3 ounces in 10 to 15 minutes, and is full afterward, then that nipple works.
You can spend a lot of money on a nipple, but in most cases, it's not necessary.
Stick with the basic nipple and have some patience with feeding
your baby. Experiment with new nipples if your baby is not feeding well with the present one.