Unless you're unable or unwilling to learn to ride a two-wheeler to the appropriate level of skill, I'd strongly suggest avoiding trikes. They're brilliant for touring and day rides (as long as it doesn't involve off-road), but are measurably slower, completely impractical on trains and force you to behave like a car in traffic.
Anything other than a very upright shortish long-wheelbase (Bacchetta Café or similar) is going to be awkward in traffic. You lose your height and flexibility advantages, which make filtering difficult. Start-stop traffic is extremely tedious on anything where you have to put a foot down when stopped, which is paradoxically a point in favour of lowracers (where you can put a hand down) and trikes. I'd suggest that if possible a very upright upwrong might be a better commuter bike. Otherwise, accept that you're going to be held up by traffic.
Beyond that, you're obviously looking at a USS tourer with decent luggage capacity and plenty of gears. Hub gears are a good thing, if only because you can change down after you stop. You *need* to be in a low gear to get a 'bent moving reliably. If the rear wheel is small, it avoids dérailleur vs grass issues. Rear suspension would be highly desirable (you can't get out of the saddle for bumps). You need a really good reason not to have a disc brake on the front, at least. Don't even consider rim brakes on a small wheel (worst case it's got to stop a loaded tourer from R17, and that heat has to go somewhere - remember that recumbents can brake harder than uprights).
You probably need to decide on whether you're going to go for features and reliability or light weight. Something like a HPV Grasshopper (maybe the foldy version) would seem like a good choice at the 'heavy' end of the spectrum. The lighter end is trickier, as you have to get quite specific about luggage requirements.
As for a decent turn of speed when you want it, that's greatly affected by how upright the riding position is. Recumbents are inherently like tandems in their weight to aerodynamics ratio, so what speed advantages you'll get will only be of use if you're happy to leapfrog any solo DF bikes you're riding with. A bike where you can change the seat angle according to the type of riding you're doing would seem like a good idea - depending on the seat design, this may or may not involve a corresponding adjustment of boom extension (which is a serious faff on most bikes).
