Well, a PCMCIA interface will be more stable but then you run into dongle security issues.
There are many people who run 24/48 over USB without major issue, myself included. I haven't tried 24/96, mainly for space issues on my recording laptop, but AFAIK at least BeckyT has done it successfully.
If you decide to go USB, be sure that your controller chip is on Edirol's compatiible hardware list. If it is, then you shouldn't have any problems once you get the drivers set up.
If your laptop doesn't have a USB2 controller in it, you can get a USB2 PCMCIA card and use that. It could be a little more stable than the integrated one in your laptop, just because of the higher theoritical bus speeds...
The dropped samples, at least in my case, were software and hardware related. I needed more RAM in my laptop and had to increase my buffers in WaveLab.
HTH