I am a big sucker for stainless steel. It's tough, and I love the darker coloring of it. (And it feels like a little badass on my wrist.)
The steel I buy is on the pricier side as it is saw-cut. This method of cutting creates a cleaner line for me to close the ring with...but it requires some saws...because it's a badass little metal.
Content: ~ 69% iron, ~ 19% chromium, ~ 9% nickel
Allergy: This one is tricky. It does contain nickel, however, for comparison, surgical steel contains anywhere from 8-12% nickel. If you have had an allergic reaction to nickel I would suggest steering clear of any steel in jewelry. My personal experience has been that my ears do not like surgical steel earwire, but I am totally fine wearing stainless steel bracelets.
I began researching the whys and possibilities of allergies and ended up in a messy, internet rabbit hole. There are plenty of blogs out there, but I'm still trying to find more scientific research. Hopefully, I'll get to this sooner rather than later. (More fascinated than anything else.)
To clean: Mild soap and water.