Here goes:
I used to own the TI2, but I've come to appreciate the immediacy of things like the Moog LP (I own it).
It really depends on what you desire. The TI2 does a whole lot, and does it very nicely. It's good at everything, but it's deep and has a learning curve. Go to the site and learn by watching the videos... Virus support is excellent. However, I found the board to be a bit clumsy and it's almost TOO 'tweakable.' I didn't like the physical layout. I was always using it as a plugin.
If you want a nice portable setup, you could get by fine with a laptop, DAW, and a TI2. Remember, the TI2 is also a USB interface. You can use it to record, etc.
I'd consider the Virus to be more of a studio/writing tool. The Moog is more for jamming, and going mad with knobs. The Moog is gorgeous for leads and bass lines. However, I have separate converters, effects, other keyboards, etc.
If you're starting out. I'd go with the Virus. Then, you got everything covered. However, if your digital pads/blips/converters/effects are fulfilled, then, I'd suggest getting an analog board.
Think bass & leads for the Moog (generally speaking). It's a one-trick pony. The Virus does everything well (even Moog analog emulations!)... However, I'd take a Moog any day of the week for messing with bass and leads.
I hope this helps.
-Phil