Yeah both are good. Basically anything that forces you to prove a lot of theorems that look trivial (but are not easy to prove) is good because they build up a system from small theorems. Back in school we use Rudin for Real Analysis and it's a good textbook. But I'd recommend taking a class if you are still in university because Math is a bit tricky for self study IMO. If you already graduated maybe follow some MOOC.
I'd actually recommend Number theory if you want more fun or if you are interested in Cryptography which is related to CS. Elementary Number Theory throws you tons of questions that even a toddler can understand but you might hit bam head on walls for nights to prove them.
Thanks, I'm doing a Masters now and I was planning on taking Number Theory and Abstract Algebra next term. I took mathematical cryptography this term and it got me interested in more related math.
