construction, not electrical. A cross section loosely resembles a W or M.
OP- the mline sounds fuller, less upper mids as I recall. Or at least that was the perception. The regular can get a little "barkier". The vintage with a twist description sure isnt far off.
I had 2 Mlines together if you can power it its really quite nice and small. One of each isnt much different, honestly. I had 2 regulars as well for a short period, and all else equal its really big for the size but cant nail the fuller bottom of two mlines.
IMO either 2 mlines or 1 of each is more versitile.
IN all likelihood, the difference isnt severe.
These cabs arent in vogue, but a pair of them is a nice wallop and tone for small footprint. I wanted just a little top end sizzle though. Not there. Also, they $are$ pricey.
hope this non-tech post helps.