in my personal experience as the chief installer and cheif designer of an audio shop, i would choose mb quart over infinity.. but i would chose focal over both of them.
IMO mb quart has a VERY VERY "SQ" sound to it. the highs are high, painfully high
the focals on the other hand have more depth and warmth to them.
i dunno if other people notice, but i do because i work also as a studio engineer, so pro audio is my life before i liked car audio...
look, listen to both, at a local shop, and pick for yourself