Purely on sound quality alone and having owned three of your choices I rate them like this..
For a flat setting C3 has upper advantages over both, especially in instrument separation, soundstage width and dynamics. The Cowon can compete when using enhancements though won't exactly meet the C3 side by side. And the Clip+ well has average detailing depth low separation skills compared and ......well I thought it was cool before trying other players.
Clip+ is kind of a benchmark for audio here, I beileve everyone should have one but not necessarily use it.
My vote goes to C3 unless you want to tinker with EQ then a C2.Edited by H20Fidelity - 10/26/12 at 4:23pm