Hi Krissy
I use the avent bottles too....from memory (sorry couldnt find any old packaging around) all the teats are "airflex". I usually buy teats from BigW or Coles and have never noticed ones that arent airflex.
We do have occassional dramas with leaks, but figured out the problem was DH would screw the top on as tight as he could....dont do this lol!! If he backs it off a little no leaks
Ive never tried DS with any other brand so I really cant offer advice on comparisons.
On thing I ony just discovered with Avent is you can get handles that will fit on any size of their bottles (no idea if other brands do this tho!)
Hope I helped and not confused you more lol