I did/am doing A-level maths, further maths, biology, chemistry, physics.
I have really enjoyed all of them. A-level goes into a huge amount more detail than GCSE. I now concentrate on the maths and physics, with biology and chemistry less important to me. They are all still fun however and I still want A-A* for each. I will warn anyone considering doing my combination that it is a lot of work, but if you're willing to do that, enjoy these subjects and have the ability, then go for it. It's been the best few years of my life so far.
I have also self-studied FP3 and FP4 and am taking STEP I-III. I wouldn't recommend these to anyone who doesn't have a very good ability in maths, but if you do have the ability, they are amazing.
Social life? If these count, we have some good discussions in lessons. I also socialise on TSR.
There's very little stress with these subjects. Being allowed to spend literally days each week doing maths is great for eliminating stress. All of my stress now comes from GCSEs.