one thing of these two amps that stick out in my mind is mostly their EQ's. the shuttle has a wider fatter sounding "Q", while the LMii and markbass stuff in general has a more narrow and nasally sounding Q. even w/ more drastic turns, the shuttle stayed musical, while not being too congested sounding. the LMii seems to get more and more harsh & pinched. the LMii's VLE knob does lessen that somewhat, but overall, i find the EQ to be more musical on the shuttle.
also, many like the VLE knob, but i wasnt too enamoured with it. seems to be more a mere blanket, rather than the "vintage" knob some tout it to be.
the LM feels faster under my fingertips. as long as the gain is set low and the preamp volume set to compensate, i can get a faster feel w/ the shuttle, but it just isnt quite as responsive. but, if you saturate the tube on the shuttle, however, you get that nice laid back glossy tubey feel that the LMii cannot do.
finally, the LM has a slight heft to its low end that the shuttle does not, which is obvious due to their different power section designs. my sadowsky's low B feels a touch more substantial w/ the LM, while the shuttle feels a little obtuse.
if you need something totally unvarnished and flat, the LM is a nice choice. if you prefer to really work your tone, the shuttle is quite versatile, while still being musical.