Yesterday I tried on both the Amp Light 45 & the Talon 44, and found it pretty hard to choose between them.
When first on the Talon felt a little more comfortable & 'softer' on the back: in comparison the Amp was a bit 'harder'. When weighted down both were comfy though.
The Amp feels like it's tougher & more rugged: the pack material feels stronger and less flimsy than the Talon, the clips & straps more substantial. Probably the slightly heavier weight of the Amp contributes to the impression of toughness as well.
I prefer the more restrained styling of the Amp: the Talon looks a little cheesy, the Amp more serious.
The Talon uses stretch pockets on the side & pack, the Amp uses thick non-stretch mesh with drawcords (potentially safer? probably just comes down to preference).
The Talon has a few more hooks, straps, pockets & 'features': the Amp is a bit more minimal & less cluttered. Again, probably just personal preference.
In the end I walked out of the shop with the Amp, but when I got home I found that the sleeve for a water bladder was to short for my 3.0L camelbak bladder - inexplicably it's only about 28cm long. According to the cascade designs website, Platypus does a 1.8L model which is about the right size (the 2.0L camelbak is still too long). But since I'd only just bought the camelbak I went back and swapped for the Talon (which has a hydration sleeve which goes the full length of the pack). If I'd really preferred the Amp over the Talon I would have been happy to stick with it and find a smaller bladder. Or you could probably mess about with the stiching at the bottom of the short bladder sleeve on the Amp.
If anyone else is having trouble deciding, I suspect you wouldn't go wrong either way :)