First of all, I wouldn't buy anything with an "i" in front of it. Not if you care about fidelity, anyway.
I've had a number of inexpensive players and they were all crapola. Aliasing galore and bass-hyping EQ whether you want it or not.
I finally got fed up and spent a little money, not for the gobs of storage (32GB, expandable to 64GB) but for the hi-fi playback quality, which is flat and full-spectrum, and with enough power to drive any headphones. At ~ 2" x 4" it's not tiny but easily fits into a shirt pocket. The 16GB version is about 90 bucks less.
Here's a
review of it.
If you do get some generic player, be sure to buy it somewhere that'll give you a no-hassle refund. You might want to load up some acoustic guitar and audition it before you get too far from the store.