Virtual Jaguar has been under development for quite a while now, and still hasn't reached a point where it can safely play most of the Jaguar's library. That, of course, is not to knock it's primary developer for anything. After all, the Jaguar is quite a tricky beast to emulate, and VJ has made a ton of headway with improvements all over the board. Regardless, though, it still leaves quite a few Jaguar titles out of my reach, which in turn makes me yearn even more for the real hardware.
Fusion, on the other hand, is an excellent emulator which emulates pretty much all of Sega's pre-Dreamcast hardware. This last week I've been playing tons of Genesis games and having an absolute blast, with the exception of Streets of Rage. Why this is an exception comes down to yet another issue with emulation in comparison to the real hardware. Stage 5 of this game has you facing off against a pair of twin sisters at the end, who are an absolute pain to deal with...unless, of course, you know the secret to beating them. I remember back in the day, my friend and I would play this game co-op and always had some issues with defeating them, but then we learned the secret. You have to lure them in by facing away and then do the "back punch" in order to actually get hits on them. Once you master this, defeating them is a piece of cake. Not so when playing via emulation, however! For some reason, I simply can NOT get the emulator to recognize the simultaneous pressing of the jump + punch buttons necessary for performing this move, which results in it working at best 1 times out of 10, and this of course leads to me being unable to defeat the bosses. Quite frustrating, to say the least.
So, as you can see, emulators can be quite fun, but they all have their limits. There's a reason why many of us prefer to play on the real hardware.