I've been using a couple different kinds of bottles, my daughter can't even tell the difference, it's totally fine to use different ones.
It is okay I use both Avent and MAM with my 5 month old son and he takes both of them :)
I only purchased Avent Natural. Babies can become accustomed to whatever you give them. I chose these Bottles because they are closest to the feel of the Breast, and I'm looking forward to Breastfeeding ♥
We have avent and a few other I don't know the name of. I am only 24 weeks but I was wondering the same thing before we buy more.