Which god spell is the best for pking?

So i'm going to get 60 magic and i'd like to know which spells is the best for pking.

neither... guthix

Sara, drains prayer.

Zammy drains mage and is most powerful, where as guth drains def.

I've used all 3 a lot for pking and i am currently using Flames of Zamorak.
Why?
First, it hits harder and is more accurate than other spells.
Second, the great majority of mages that go pkin don't have 85 magic for teleblocking yet OR they are a little over that(if not exactly 85). My point is, If you find another mage on wild and you are using flames of zamorak, the first thing you have to do (before casting teleblock), is to cast flames of zamorak. It will drain 5 magic levels, that means you have a great chance of not getting teleblocked during the fight.
Third, God spells only drain 5 levels and they only drain it ONCE during all the fight. Do NOT go to wildy with Claws of Guthix thinking that you will low your oponent's defence to 0, or you will end with your oponent's prayer very wuickly if you are using Saradomin Strike. Flames of Zamorak also won't make your oponent's magic to 0, but it will help you in other ways.

If I were you, I wouldn't go pkin with only 60 magic. God spells are very good but only if they are used with Charge (level 80 magic required). At your level, the best thing you can do is Iban Blast, that hits up to 25. When you reach 80 magic or 76 (potted), go for Charge + God spell.

Wow! Thank you for that information, it is quite helpful.

I'm using iban blast too....but what's the best advantage of charge? what does it exactly do? You can hit 30's without charge? or not?

Flames of Zamorok is the strongest. Right now i am using Saradomin Strike. If you have charge, you can hit around 30s with god spells.

The uncharged max is 20, whereas the charged max is 30.

Charge > uncharge.

^^

Also, Tamarindu also explained how they work.