Nexus 5: decent but too quiet on my sennheiser hd360's. Clean and detailed but needs about 20% more headroom
HTC one: nice and loud with beats audio turned on. Very subtle EQ and pleasant with most types if music. With beats audio setting turned off still good but I'm pretty sure there's still some other EQ being applied. This phone isn't for the purist.
Samsung Galaxy s4: I've actually sampled two of these and they sounded different. The first was awesome, like "my music never sounded so good" awesome. The second unit was still good but something was missing. Not sure what but not as engaging. The second one may have been on newer firmware .
IPhone 5: Very accurate almost sterile sound. Not enough volume though. Couldn't drive my ety er4's efficiently.
IPhone 5s: OMG nearly perfect! Clearly the loudest of them all and pristinely clean unadulterated hi-fi. This is your benchmark.