i have this doubt too when i have to choose, and thinking on the price, the difference of performance and etc...and i think is better go to the G3...for many reasons:
1st: screen percentage to body ratio is better than the G4,
2nd: They perform similar, have the almost same specs, SD808 over SD801 dont worth the overpayd money.
3rd: Isnt curved, you dont feel much curve in G4 but G3 is flat...and is good to handle.
4th: They will have the Android Marshmallow like G4.
Is my opinion, i have the G3 since March and i love it, already play with G4 more than 10 times when i go to shopping center and i dont feel the same as i feel with my G3...go for it, worth a lot better the money you pay for the G3 over the G4.