If its for only for swimming then for ease of use the SWIMP3 is the best choice from my experience in the pool.
If its for swimming plus other activities (like the jacuzzi) my choice would have been Nu Dolphin as its versatile and has the best designed earphones for swimming. However I now believe that in 2011 from experience of selling the Splash Gear waterproof mp3 player its is now a better choice than the older NU Dolphin player both in terms of reliability & ease of use.
Another choice for swimming only is the Speedo Aquabeat its controls are easier to use than the NU Dolphin but the earphones are not as well designed for swimming as the Nu Dophin. However in 2011 Speedo have now attempted overcome these design issues with new headphone styles for the standard Aquabeat
If you buy a Speedo Aquabeat you can buy additional earphones like the ones by Aquatunes that are a better design for swimming and Speedo have similar additional earphones on offer. These are the barbed conical style plugs like ‘christmas trees’ that I think work best for swimming.
Please see this answer to a customers question
The Finis SwiMP3.1G waterproof MP3 player is my first choice simply for ease of use when swimming. It is a waterproof MP3 player specifically designed for swimming. You can change track without breaking swim stroke I do this by turning over from front crawl to to backstroke then pressing button at side of my cheek & music track is changed in one swim stroke then I flip back to front crawl.
Standard waterproof mp3 players rely on the transmission of sound through air or water causing the swimmer to be reliant on the quality of their earplug seal. Any break in the earplug seal means that water enters and causes the sound quality to become muffled. However the SwiMP3.1G uses bone conduction – the direct transfer of sound vibrations from the cheek bone to the cochlea in the inner ear – to provide the swimmer with exceptional sound clarity.
Moreover bone conduction may be safer (researching this assertion) in the long run than using normal earphone based MP3 players. The European Commission is expected to demand lower default sound levels for all MP3 players sold in Europe. According to the EU’s scientific research arm listening to MP3 players at high levels for an hour a day can lead to permanent hearing loss in five years.
Finally SWIMP3 is my personal choice because..
However I would recommend NU Dolphin 2GByte waterproof MP3 player with earphones if you are going to choose one that uses earphones as my next choice based on its reliability. Although some of my customers have had problems with left earphones failure on NU Dolphin units the product is well supported and the earphones are well designed for swimming & staying in the ear (Christmas tree style long tapering conical barbs)
Then I would choose the Speedo Aquabeat as its controls are easier to use than the NU Dolphin but I believe the earphones are not the best design based (mushroom type) on a few my customer feedback experience
Finally as of September 2011 I must state again that I now believe that in 2011 from experience of selling the Splash Gear waterproof mp3 player its is now a better choice than the older NU Dolphin player both in terms of reliability & ease of use for a waterproof MP3 player that uses headphones
Hope this helps