Necrokick!!!
Anyway, I've only played one Oracle with the Nature mystery. Kinda cool but probably wasn't the best choice as it wasn't really conducive to my playstyle.
I can't really tell you what mysteries are the BEST mysteries but I can give a brief synopsis of what some of the most 'renown' mysteries can do:
Flame: Blast things. You get some of the most notorious blast spells in the game with this one. See the world burn around you while still be capable of healing your allies during your down time.
Heavens: Shut down EVERYTHING with illusion(pattern) spells and get some really nifty powers and perception as a class skill.
Metal: Become a better tank they your fighter and become a better party face than your party bard.
Battle: If I need to tell you what this Mystery does, look elsewhere.
Nature: Ever wanted to dump Dex and have a mount and have some druidic skills without the inherent complexity of playing a Druid? Yo.
Bones: Necromancy ahoy! Raise dead things and make the living regret ever challenging your divine authority with SoS spells. You also get all society skills and stealth from this mystery as class skills and stealth. Lot of possibilities.
Wind: Crowd Control shut down mystery. It's pretty straightforward. Later on you get some very mean spells.
Life: Party band-aid with the option of becoming an Elemental subtype with lots of utility. Plus, if you life channelling then this is your mystery.
I'll leave it at that for now. But it really depends on what you want to do with the Oracle.
