I like the Zen Stone, and I think the iRiver T60 sounds better (and it can be EQ'd, unlike the Stone, which I haven't bothered with yet).
The Stone (1GB) is very pocket friendly (together with canal phones, it weighs almost nothing) and affordable, and the newer Stone Plus (2GB) would be quite a deal and equally as pocketable. Very easy to operate in a pocket or without looking at the player. Without any kind of case, I can keep it in a shirt pocket and not really tell that it's there.
The T60 is bulkier, but then most players would be compared to the Stones. (The T60 fits OK in a shirt pocket, for example, but I know it's there.) The AAA battery can be an advantage in certain situations, and at 1GB, 2GB and 4GB, you have a choice regarding capacity. I got the 2GB for $80 online, and it's an excellent value.
If I had to choose between the two, I would base my decision on whether I wanted a sleek, tiny player with a built-in battery that needed to be recharged via USB ... or a player that uses AAA or rechargeable AAA batteries, which can be useful on the go or when away from computers. Yes, the iRiver sounds really good and is more tweakable, but I have no complaints with the Stone's sound.
_______________________________
Sources (in order of purchase):
2nd Generation 10GB iPod for Windows (retired)
Creative Muvo 256MB
Creative Muvo 1GB (out on loan)
Rio Carbon 5GB
Cowon iAudio 5 1GB (out on loan)
Rio Karma 20GB (low-mileage collector’s item)
Creative Zen Nano 1GB
Samsung YP-U2 512MB
4th Generation 40GB iPod (monochrome; used as home jukebox)
2nd Generation iPod Nano 4GB
Creative Zen Stone 1GB
iRiver T60 2GB
