i like NUK better. find that avent ones are to "rounded and big".
it takes time to train them to suckle on pacifier. i gave my little one since less than one month because he is too fussy. he has slight nipple confusion but manage to adapt as time passby.
initially very fed up because they will keep pushing out, but i keep trying and trying at different times till he knows how to suckle. need patience , do not force him to suck at one time as it will create frustration, just few attempt many times thrghout instead. they will sure to suck and drop the pacifier countless times