With my son, I nursed and used bottles for pumped milk.
The ONLY bottle that I and he loved, was the "MAM" brand.
You can find it at Amazon.
It is not widely found in stores.
It is also, BPA free and does not accumulate air bubbles in the bottle as the baby drinks. ie: no gas from the bottles, and it is a natural nipple.
This bottle, is commonly used in Europe.
Its also real cute, comes in different colors, and sold in 3-packs and is not expensive. Very easy to use... and clean.
I found Avent... to be not as good. And the nipple is so bulbous... and not natural.
Next: it could also be that your baby gets "nipple confusion." Because, drinking/sucking from breast, is not the same as from a bottle. A bottle is by gravity only. From breast, is encompasses mouth/tongue coordination and 'sucking' to get the let-down going...
all the best,
Susan