My favorite set is 1975 for a few reasons:
1) They're the first packs I opened as a kid.
2) Simple design with awesome colors.
3) Lots of good RCs including two of my all-time favorites, Keith Hernandez and Gary Carter.
4) Tons of HOFers in all stages of their careers...Aaron, Ryan, Schmidt, Seaver, Brett, Yount, Rice, Gibson, Fisk, Rose (Technically not HOF, but c'mon), etc.
Your points one and two are exactly the same for me. 1975 Topps is a quirky looking set, but I love it. I completed it last year, and I love flipping through it occasionally.
My favorite none Topps set is the 2002 Studio (one day I will post everything I have collected over the years). Not a huge RC year, but the patriotic theme and the inserts subsets are on the lower end, so for me, very collectible.
Todd