I have owned both a POD 2.0 and a J-Station for about 4 years. The J-Sation can be a "better" sounding unit if you have the software and learn how to use it (and the digital out can be a welcome feature for those who embrace that side of technology). However, it is very limited as a stand alone unit (if you buy a used J-Station make certain you will be getting the software).
I prefer the POD mainly because it is easier to use without editing software (although for deep use you do need to use the POD software) - Candidly, I think you can get plenty out of the POD without the software.
I purchased the POD and J-Station because I didn't have any decent amps and would not have known how to dial up good tone even if I did have amps (my main axe is drum kit, followed bu jeys). During the last couple of years I have purchased, rented and/or borrowed various amp/cabs/combos and little by little I am learning what so many have said since the start of emulation - the emulators simply do not sound as good, as punchy, as articulate (chosse your own words) as well mics cabs. And I was always willing to speak in support of emulation.
The lack of brightness, sparkle, depth, mentioned earlier in the thread - is what is wrong with emulators. With a certain amount of tweaking you can dial more tone in, but it still ain't a real amp. Note: I have run my POD/J Station though a BBE "sonic maximizer" and it has made a world of difference (I worked with a real good guitar player who used a BBE in his live rig and I was very impressed with his sound = so I tried one in my guitar "recording chain).
I still think emulators have a place - in particular for people who can't blast a cab do to young children or worse, old neighbors. I use emulation more than real amps - mainly because I live in a condo - but lack of shimmer in the recorded tracks is a very real potential concern.
It has some really nice sounds!!!!
I actually ran it via spdif for awhile into a digital roland mixer and into my Alesis Monitors and the sound was awesome. Much better than analog
Running it via an Uno midi to USB cable gave me access to the J-Edit program on my computer which was great for doing deep level editing easily.
Santa brought me a PODxt which is a very nice unit but is requiring me to edit sounds to add the "sparkle" mentioned above.
Then again, I've always played my Twin with all the EQ knobs at "6", so I was never into "shimmer" much. None of the preset amp models sound that great, but The Fender Bassman model sounds more like my Vintage Twin than my Vintage twin when I mic it. (if that makes any sense.)