I'm with SuMz on that, I try to avoid libraries for studying when possible for quite a few reasons.
However, I like Innis the best, but the others are okay
1) Innis - close to all my classes, study rooms are legitt
2) Thode (far away from my classes, kinda dirty in a few areas, lotta garbage everywhere from my experience)
3) Hsci, nicest library, way too crowded tho
4) Mills, crowded, dark, not my fav atmosphere.