It all comes down to personal preference. I have 8 players now (2 x Clip+, 1 each of Cowon S9, iPod Touch 3G, Sony E353, Creative Zen V Plus, Nanite N2, Fuze v1). To me, that is the best way to go to find out about the "best SQ", because I can compare using my own ears. Audiophiles feel differently about each player (iPod sucks, Cowon is great, Clip+ is waste because it ain't got much power). To me, none of them have the "best" SQ, I just
prefer Clip+ better, that's all. The difference in SQ is marginal between players - signature differs a bit between each player, but I doubt if I can detect each of them using a Blind ABX. What matters more is the ability of players to drive IEMs. Most portable players do not drive headphones satisfactorily. Some struggle a bit with Balanced armature IEMs and a few with current draining IEMs. I find Clip+ to be pretty decent across, but battery life and output power are two concerns. Fuze+ should be better with battery, but output power should be around the same ballpark.
For a player, ease of use, navigation, file format support, battery life, size, weight, storage and support for expandable memory, output power - matters more than absolute SQ. The often misused "SQ" is at best decided by your own ears. For instance, this
brick is said to have better SQ than all of them - and I might try it someday. But, it's day-to-day use is another matter altogether.