I'll admit I like the greenbacks of various notes more so than the front usually, unless its a star note or has a cool serial number.
I been loving the funnyback $1 back ever since I started collecting and now trying to acquire a 1928C and D $1 funnyback in UNC grade.
The $50 back with capitol hill is also another favorite of mine especially those from series 1928 to 1934 A.