Best Approach for Email Sync Method - Token or Push or Others

Dear Team,

I am planning to build Email Client APP on Android Platform. which has syncronize features.

i would like to know what is the Best approach for Email Sync. can we use Token Based or Push Method or is there any other method ?.

and also which method will provid good Performance and less battery consumption ?.

Could you guide me on this as early.

Thanks in Advance.

Regds,
Rajesh. S