jackd --sync -Xalsarawmidi -dalsa -r48000 -p256
a2jmidid -e
still is the way I go, when using jack2. Regarding MIDI jitter I don't
know if nowadays something better is implemented for jack2 and/or jack1
or if jack1 nowadays provide alsarawmidi too. I guess you need to test
all available options on your own. IMO you shouldn't use an USB device
if you care about MIDI jitter, this seems to be the weakest point in
your chain.