What god is the best on pocket god?

That depends on opinion. Of course, perhaps the most important thing to consider is the power. Some idols are pathetic, like:

Shark God

All Gods with the "Freeze idol for 3 turns"

Globe God (although this may just be due to me not understanding what on earth it's supposed to do)

The above are not good idols to use, as their power is either weak or does not increase, like you'd want it to.

In my opinion, it depends on what you prefer. These are my top idols.

Zombie God - buys time, so you can use your other awesome powers!

Monkey God - massive damage, and for two turns!

Turtle God - not the best defence increase, but the reflect ability is invaluable at a higher level

Underwater Pyramid God - good attack increase and reflect value

• a very useful idol

Something like a tie damage effect would also be good.

Annal and Deva are also good. Annal is amazing if your others also have amazing power. Deva is adequate too.

A one off damage effect is often powerful, and is very useful as a result.

In terms of realm, I can't help you there. I'd just make sure you have a wide base of realms and attack types; this will ensure that they will never have an idol with total advantage over your selection. For certain battles you would find it easier if you designed your team as opposed to using the same one constantly.

The best overall, I'd say, is the...Monkey God. If you get the effect AND attack, and the attack next turn, you will so quickly win that nothing else will be necessary.