While I don't have experience with either the new Zoom or the Presonus Firestudio, it looks like choosing between those, other than the bit of cost difference, would be portability. I think the Zoom stuff would be a little more portable.
The Firestudio requires a PC with a firewire port and you may have to get a firewire cable. Many newer laptops come with a firewire port but if you were thinking of using a desktop system, you may have to purchase and install a card. Outside of those items, it looks to be pretty nice. Look closely at the system requirements before using any old laptop. New laptops will have the memory and processing power necessary but those just a few years old may very well not.
Interesting option, though. I myself, like you Emoto, use the H2 for recording jam sessions. I basically try to set it up "in the midde", turn on double stereo recording and let it rip. I picture the other Zoom units as the same and have been looking at buying one. That amongst other gear I just haven't pulled the trigger on yet
. So I was looking for the situation that you just set the mic levels kind of even and low enough not to distort and just hit record, stop and save, record, stop and save type thing. Worry about maximizing the envelope and adjusting the track levels afterwards. I started reading the manual online to determine if this method is feasible but that is another project in the works.
So I guess to some extent, usability comes into play also depending on what you are looking to do. For me it is record jam sessions, loose and free. For you it might be more of a studio situation with more structured approach to the recording and such.
Good luck with it. I am sure either the Zoom or the Presonus Firestudio would be a good solution for you.