yeah as Err0r said, it is obviously a matter of opinion. However.....here are a few which have been highly praised and should fit your criteria.
Sony NWZ-A828K (whole 820 series)
Sony NWZ-A818 (whole 810 series)
Sony NWZ-S610 (whole 610 series)
Cowon D2
Iriver Clix 2
Samsung P2 (does not have drag and drop file transfer though)
Creative ZEN (may not have drag and drop file transfer either, can't remember)
iAudio 7
From personal experience I would reccomend sony players highly, they have great sound, great build quality & great battery however they are pricey. They have just released a new 16gb model in the 820 range that looks very nice. The Cowon D2 is also a favourite but again is a little pricey. Also check dapreview's poll section for info of what members voted as the best daps.
DAPreview.net: MP3 Player News and Reviews
I can understand ur frustration with the M3 though, I have wanted to buy one as a small player for use when excercising for a while, but the stuttering has definitely put me off, I prey they fix that soon. Other wise my next meizu purchase will be the M8.
hope this helps...