Of the commercial aircraft currently flying passengers in regular service my favorite is, without question, the 747-400. For me there is nothing more magnificent in the skies - the power and stability; the ride; the elegant, stately cruise - truly an impressive aircraft.
Having said that, I still am quite fond of the L-1011 and DC-10 (as well as MD-11) and have wonderful memories of the 707, DC-8 and 880. Also have to say how much I love those occasions on a 757 when full power is used on takeoff.