I used to store my BM in glass bottles but gave up on them during my early breastfeeding journey as they occupy too much space unlike breast milk bags which I can freeze them up neatly and stack them up properly. Bottles are effective and economical if you are rotating the milk out to be fed everyday thus keeping the space they occupies as it is. Not a good idea if you want to keep them in bulk and to create space you have to keep packing and stacking and removing/donating them. Even if you get a stand alone freezer, spaces fill up pretty quickly. I would still prefer milk bags when I want to build stash.
Depends on what u want to do with the milk. If u are not freezing the milk and not building a stash, then milk bottles. Otherwise it would be like what the lady above mentioned. I dun have a lot and I never build stash (I am temp a SAHM), so I just put in bottles, if run out of bottles Caz forgot to give bm, then will use milk bag - but there is the washing and sterilizing which is not that bad because u can do it when u are washing the milk bottle anyway