My personal experience struggling with bottles
Avent - initial I tot the bottle leak, actually I forgot to put the ring, so I swop to those yellow anti-colic bottles where u don't need to put the ring. Dont turn soooo tight else the air won't flow well or teat will compress. if ur milk is very hot, make sure u open to let the hot air out before u close the bottle den feed else u keep seeing the teat compress too, I usually hear a sound of the air flowing when my gal is drinking smoothly.
I use their sterilizer as well, easy n convenient for my n hubby.
Nuk
I like their bottles cos there's cartoons n I tried both types , but the problem is the hole u mus use scissors to cut wider n after a while it doesn't work smoothly for my gal drinking n she drinks slower wit this n always end up nv finish becos milk turns cold. Usually she drinks up in 2-3 mins.
My gal don't have nipple confusion, whichever bottle I gave her on nuk or avent she jus drinks.