Hmm i would always go for the phone with the most recent to market date, which would be the zenfone 2, plus 4GB ram is really a draw for me. BUT, battery life is dismal on the zenphone 2 right now. Not sure if future firmware updates will fix it?
At my current usage pattern - 4G off most of the time, whatsapp, wechat, line, skype on push all the time, 3 email accounts set to manual refresh which i do every 1-2 hours, minimal SMS, 15-20 mins of outgoing or incoming calls, 2 hours of music playback, 2 hours of e-book reading. I need to charge the phone once at mid day to ensure i have enough power to last till i get home, usually 9-10pm at night. If not the phone will be dead by 6pm.