this is subjective. Do you want android or IOS. Really depends on your preference. My opinion, the iPhone 4s is very outdated and a crummy phone. Also, i prefer android, as i can multitask, customize, more/better apps, add storage, etc.
With that iPhone, you are limited to the 8gb only. With an android phone, you can ad a microSD cardl. Both have non-removable batteries, which is a HUGE downfall and would deter me from both.
Not sure what you want to pay, but I would pay, and to me it looks like you want a smaller phone, may want to look into S5 mini?