to control a DAW like ableton live with a midi keyboard like the axiom, wich type of connection between USB and MIDI is the fastest, will give me the lowest midi latency possible??
USB is hundreds of times faster than midi but the way USB works, midi over USB generally works very poorly. I would try both ways and see which works better, but plugging in the axiom into the delta would probably be a better solution than using the USB
if latency is a problem, you can adjust it in your audio settings, tweak your buffer setting by lowering it little by little. If you still have latency problems, then look into a midi interface, that will solve it all.