Largest 747 operator:
ANA isn't but JAL definitely is, JAL had at one time close to 100 B747's!!! JAL was the very first airline, with Pan Am, to order a bunch of B747's back in the late 60's when the type was launched. But you're quite right, if you look at JAL and ANA combined, one 747 out of seven is built for a Japanese airline.
In America: the two largest 747 operators are Northwest and United. It used to be Pan Am.
In Europe: the largest one is British Airways.
In Africa, it's South African Airways.
Largest 737 operator:
I also think it's Southwest, and Continental.
Largest 727 operator:
FedEx probably is today. At one time, United was, with over 180 aircrafts. Don't you remember when United had over 180 B727's? Fifteen years ago, American had 164 of them. Delta also had a lot of them, when they purchased those from Pan Am and Western.
Largest 717 operator:
I think you're right. It must be Air Tran. It was going to be TWA with a 717 fleet of no less than 50 aircrafts, but we all know what happened. Midwest Express also must have quite a few.
Largest 707 operator:
I think it was American, during the 60's and 70's. TWA also had a lot of them until the early 80's.
Largest 757 operator:
I would say American and Delta, they each have over 120 of them. United has close to 100 of them. The largest non-US operator of the type has always been British Airways.
Largest 767 operator:
It's definitely Delta, their 200/300/300ER/400ER fleet combined comes up to over 80 aircrafts.
American is the second largest 767 operator worldwide.
Largest 777 operator:
It must be United, with a fleet of over 50 aircrafts. American must be the second largest 777 operator in America.
In Europe, it's British Airways.
In Asia, it's Singapore.
But once all deliveries will be completed, who will have the most worldwide? United or Singapore? That, I don't know.
Largest DC-8 oparator:
It used to be United.
Largest DC-9 operator:
It's definitely Northwest.
Largest DC-10 and MD-11 operator:
It's definitely Fed Ex.
Largest MD-80 operator:
It's definitely American, it was alrady even before acquiring TWA!