I don't think it's an issue of "talking someone into" firewire - it's just another option. If you were planning a setup in which you needed many inputs at once, I would absolutely recommend FireWire over USB. When you're recording a track or two at a time, USB will do just fine. The units you originally mentioned are good. The Tascam 144 would probably be my pick, but that's because I've owned several Tascam units over the years and always had good experiences with them.
I bought an Emu 0404 but I wish I didn't
Can't really handle a guitar. No true Hi-Z input. Loss of high freqs.
Otherwise very good, but not guitar suited.
Don't know if a Tascam can handle guitar? Clean samples anyone?
And maybe mike samples too, because I would like to keep the high E-mu mike standard...