It is almost one sided battle , Asus Zenfone Selfie is better in every aspects
Asus Zenfone 3 has the following advantages over Oppo A37: -
1. Asus Zenfone Selfie has faster and octa-core processor. 2. Asus Zenfone Selfie has 3GB RAM while Oppo A37 has 2 GB RAM only . 3. Asus Zenfone Selfie has bigger screen (5.5 inches) and better screen resolution .
4. Asus Zenfone Selfie has 13MP Camera while Oppo A37 have just 8MP Camera.
5. Asus Zenfone Selfie has 32GB Internal Memory while Oppo A37 again just have 16GB Memory.
6. Asus Zenfone Selfie has bigger battery and hence longer battery life.
Verdict - In my opinion, Asus Zenfone Selfie is a better phone in overall performance
My friend has Samsung Galaxy ON NXT and he play lots of games , no lags , cameras are also good. I would suggest this phone as per your requirements coz it also support upto 256GB expandable storage. However you can check comparison of these phones here