I'm thinking most popular would be the 737, but I have no idea about least popular. (Tu-144? ;D)
My guess is that for MH the A320-200 is the most ordered plane in the game. For LH i would think it is the A330-300. For SH i've seen many discussion on the forum of which plane is the best, so here i can't say with certainty which plane if the most ordered/best plane available
Most popular Concorde and 380. Everyone wants to order them but few do
In GW2 the Fokker 100 is the most produced 7,500ish, and has more orders than the second most A320-200 7,000ish. 737-200A 6,400, 737-300 5,500ish. However the A320 series has more produced 13,000ish than F70-F100 9,000ish. DC-9 is right there at 11,000ish, BAC1-11 9,000, 727 9,000ish, 737-1/2 9,000ish, 737 Classic 9,000ish
LH, DC-8, 767 are both 7,000ish. 762ER 3,200.
Lots of A/C with no use.