Out of the box that would be the iphone 4S (my Dad hs one and it sound good...not great but good) but if you root the Samsung Galaxy S (not S2 that sounds terrible) and use the Voodo app then that would be the better option over the iPhone SQ wise though the Galaxy S is becoming a bit dated!
Your best option IMO would be to get a dedicated DAP like the Sony Z1060 (or Z1050 smaller size 16GB) its android aswell so you can still get apps and watch movies etc with it...i currently own a SGSII and the Z and can honestly say that the screen on the Sony is better (same size not sure about resolution but the Z definatly looks crisper with more accurate colours) but it honestly sounds AMAZING the headphone out sounds better than my old RWA iMod connected with ALO LOD to a Fiio E11 thats crazy for such a slimline product that has soooo many other functionalities too! (if you do get one make sure you buy outside of EU to avoid the volume cap...i wish i had done this!)
The thing is with using phones for music is there not designed solely around audio unlike dedicated DAP´s...hence why Sony´s phones don´t use the same amp that the walkman Z does, would be way too expensive or bulky or both!
Or if your worried about staying light you could get a Clip+ or Clip Zip (both have same SQ) they are meant to be very good and there so small with micro SD so cheap for large storage, but never heard one so cant comment...would give you better battery life having phone and audio seperate! if you go this route then you may have enough money to buy a SGSII aswell (look on ebay or somewhere similar for those people that get an upgrade and then sell their phone...thats what i did as you still have the warrantly in your name!) with this you would have IMO a better phone than the iPhone 4S (if you root it) and better or similar SQ with the Clip+ (will have do look up iphone4S vs clip+ to be sure)
But i do see the appeal having everything together as one unit and if thats what you want then iPhone4S is for you!
Edited by danny93 - 4/12/12 at 2:33pm