From what I hear there is no major performance difference between the PC Card AverTv and the USB one. USB 2.0 is about the same speed as PCMCIA. The PC Card one is smaller and doesn't dangle off the back. I use Firewire for digital input, but for analog input the Aver works as well as I need.
That said, there are more USB tuners than PCMCIA. You can get a proper HD USB tuner, and there is space for more ins and outs and doo-hickeys.
But these are still software dependant so you need a gutsy lappy. To really make life easier a card with full hardware MPEG/AVI conversion is the go, like one of the Canopus cards.
So while the Aver card works very well for the money, and very well for my occasional transference of analog video, if you want the ultimate it will cost more and be much less convenient.
Just to twist in the wind again, however, more and more lappies are coming with built-in tuners/video inputs and they will only get better. So i wouldn't spend up too big.
Cheers
Steve