16 Ohm means less resistance than 32 Ohm, so all other things being equal, 16 Ohm headphones can sound louder, but also place bigger strain on the amp as the amp will now be delivering more current. Depending on the amp, this may result in audible distortion if the amp can't handle such high current.
However, "all other things" are typically never equal - you've got different speakers/drivers in each headphone, different sensitivity, etc. Best is to just audition them all and then decide what sounds best to your ears. Volume is just one parameter, but there is a lot more to sound quality, and a lot of it is personal preference based. Then there is fitment, especially when it comes to earbuds or in-hear phones. All our ears are shaped differently, so what fits me may not fit you well.