S.R.
Best bet is to get several different kinds (don't "stock up" on any, just one of each) and see if there is one your little one takes to more so than the others. My 2nd didn't take to the same kind that my first did, and it took me a bit to figure out to try something else... :)
ETA: I forgot that with my 2nd I also had to warm the bm up to slightly warmer than I thought it should be.