I also useing Avent to feed my bb, the design of the nipple is for breastfeeding bb and nipple shape is close with mothers nipple. You can consider this bottle and it is easy to mix milk powder.
When I go to see doctor, I read the book which introduce the Dr. Brown bottle and it is best bottle for bb and very good gas circulation inside th eDr. Brwon bottle. I know this bottle {Dr. Brown} 會漏奶 when milk temperature is too hot.
try "nuk" or "gerber" , more expensive but it's very good. Don't buy those colourful bottle as afraid colour will fade out after several steam and wash.