Which is the best non-steroid OTC medicine for muscular pain relief?

The one that works. Other than tylenol, (acetaminophen) otc pain meds are all in the NSAID class. Although they have similar mechanisms of action, their efficacy is variable from person to person, so you just need to see which one works best for you.
Tylenol, (acetaminophen) NSAIDs. Tylenol (acetaminophen) is probably the "best" because it works for some people but is much safer than the nsaids such as aleve, naproxen, ibuprofen, etc. To be safest, don't take more than 2000mg/day if taking for a long time, and don't combine with alcohol. As far as anti-inflammatories, aleve (naproxen) and Ibuprofen (advil) are the main ones. Some people respond better to one NSAID than another.