Best waterproof MP3 player?

Hello, Searching around, Ive seen this is the biggest online forum for swimmers so I might as well ask here as I imagine most on here are experts.... Im looking to give as a gift in bit over a month a waterproof MP3 player. Now, she simply swims for exercise, not nothing professional or/and for competition. She will mostly use it in pool but I think it would be nice for it to be "ocean-ready" as well although this isnt a requirement. Size, Im not sure if it matters if it is 4GB or 8GB. Besides that, Im not sure what else information is needed to ask. Thank you all for your replies.