I have a copy of both Spivak calculus and Apostol.
I use both from time. However, I find some of Spivak's problems just boring. I was thinking of maybe trying Abbott.
Especially for continuity proofs, I want a book which slowly, progresses from easy to difficult proofs, because Spivak is very fast, and very difficult. Most of the time I cant do Spivak problems.
So should I give Abbott's Understanding Analysis, a try? Or is Spivak better?