Well I don't know about new valve manufacturers or some of the so called stainless products out there but:
- you can usually tell a good intake martensetic (hardend) valve as it is magnetic. Will not deform at intake valve tempuratures and wear well on hardened seats.
- good exhaust valves should be non magnetic austenetic steel.  Although softer they handle higher temperatures of the exhaust.  Martensetic valves on the exhaust tend to break.
Some manufactuers are using austenetic steel intake and exhaust.  Personally, on older engines, I have not found these to last as long.
Some of the steels out there today say one thing and are actually another.  I tested an 8.8 10 mm bolt and found it to be 4.8 at best.  Many aircraft and higher end industries are  buying only products with test certificates for just this reason.
Good Hunting