Oh, GW 90, 75, and 60? I'm impressed that anyone here even knows who 75 is, but there's one more you're all forgetting who probably has the most storied history of the surviving GW fleet. Let's have a look at what the four surviving engines, including the one nobody mentioned yet, have gone through since their retirement from the GW...
90: Last engine to leave the roster in 1968, lives a prosperous life at the Strasburg Railroad, probably the most well-known GW engine
60: Sold to the Black River & Western in 1963, where she lives a happier and more useful life than on the GW, got a well-deserved spurt of popularity upon recent restoration
75: Bought by Everett Rohrer in 1965, starred in tons of movies including Breakheart Pass and A River Runs Through It, sold to the Heber Valley Railway when Rohrer died in 1995, awaiting restoration with UP 618, somewhat known among railfans
51: Bought by John Birmingham in 1963, starred in movies like Cat Ballou, ran the last steam train on the D&RGW Moffat route, mothballed in the 1970's and restored in 1982, pulled excursions on her home rails in the late 80's, attended Steam Expo in 1986 and Washington Steamfest in 1990, ran on the Fillmore & Western and hit even more film gold from 1993 to 2003, re-bought by John and stored in the Hudson Terminal, ran under steam in 2009 and is steamed up every year, almost unheard of among most railfans today
That and several other factors make GW 51 one of my favorite steamers. At the very most, she'd place third behind two engines which represent the pinnacle of late steam. My second favorite is C&O 614, as she managed to do over 80 miles per hour with over 20 cars on some trips, pulled loaded 100-car coal trains at over 50 miles per hour, and represents what is considered by many to be the most modern steam locomotive ever built in the US. The only thing it's missing is sentimental value, and my #1, N&W 611, has that. I fell in love with her for her dazzling looks in I Love Toy Trains when I was a tiny tot living in the Garden State, but when I heard that her and her sisters could pull two passenger cars up an 8% grade and still maintain 20 miles per hour and pull 15 car trains at 100 miles per hour without throwing rods and valve gear all over the place, my opinion of her grew from admiration to mad, passionate love.