We started using Avent bottles and then used Dr. Brown's but found our daughter did not like to go back to Avent bottles so we have been avid Dr. Brown bottle users since then!
They are a lot more work - cleaning all those extra parts takes time - but it seems are daughter greatly preferred them and never had problem with colic,burping etc.
My son used to use Avent but have problem with burping. Now we switch to Cr Brown and problem is solved. It takes more time to clean each part but worth the effort.
my daughter is 6 months old and have been using Avent bottles and there's been no problem. Also, Avent has other products like their Sterilizer and bottle warmer etc that is great so if you use their bottles, everything will be compatible too!
The Avent bottle warmer also works with Dr. Brown bottles. I use Dr. Brown ever since baby was new born. Have not tried anything else so cannot compare.