I had been using Medela just because it's easiest - I bought a "calma" but baby really doesn't like it. I just bought a few "comotomo" that seem to be working well, and are simple to put together. I can't deal with the ones with a zillion parts.
My baby is 6 months and still does not take a bottle well, but when I use one I use the Nuk bottles. I have had better luck with those because the nipple is shaped like my baby's passie. I use a slow flow nipple. I've tried several kind and found he likes these the best. My daycare provider has started puting my breast milk in a sippy cup because my baby doesn't like the bottle. He will eventually take it they just have to really work with him.