Well the liners are not unsafe. They are very safe to use! I have never used them before though. And I do believe they do get less air with liners as well.
I like the kind with the plastic drop in liners.
maybe it's un-politically correct these days, but there's a lot less to wash and if you're interested in breast feeding that means that you can pump into the plastic bag, refrigerate/freeze it, thaw and drop it right into the bottle. (they make liners especially for doing this so I can't really see it being unsafe)
and I don't know if it's true or not, but I also feel like the baby gets less air with the liners...
BTW, I used Avent BEFORE I knew they were unsafe!!!
Well there is a recent debate about hard, plastic bottles containing a chemical that can leach into the milk. I personally used Avent with both my girls and loved them. However, they are on the list of unsafe bottles. I believe the chemical is bisephenol-A or something like that. Just google "unsafe plastic bottles" and some lists will come up for you!
The best bet is GLASS bottles.