| I have both, and have clips up of both on my youtube channel with a couple of different cabs and basses. Both sound great, and both have their own tone:
LMII/III... total plug and play, relatively flat, transparent beauty.... relatively even from the mid/low bass all the way up to the sizzle region.. loud, light, inexpensive, great EQ (the filters are awesome)
RH450... features, features, features... storable presets, compression, tube overdrive, four bands of semi parametric EQ, headphone amp with stereo input for iPod, tuner, mute switch, awesome DI... whew! Amazing. More vintage... chewy, low mid punchy, a bit vintage and old school sounding (i.e., a bit attenuated in both the deep bass and upper treble, just like 'back in the day'). If you are a doubler, the presets, which store pregain, effects, post EQ volume, EQ, compression, tubetone, etc. is a dream!
Both are just fabulous, loud as heck. The RH450 is a tweaker's dream, the LMII/III is a player's dream (i.e., if you just want a darn great 'out of the box' sound and don't want to screw with anything other than a few tweaks for the room acoustics), to oversimplify.
I love them both! | 
