Now its the era of smartphones. So its betyer to buy a smartphone rather than a budget phone.
OS : Its better to go with android or ios. Android is the best option since it is very much user friendly and customizable.
RAM : Its better to have a 2gb ram minimum. Now high end apps and games are available and its better to have minimum 2gb so we can use without any lag and provide us a smooth performance.
Processor : A minimum 1.5ghz octa core processor will be a good choice. Snapdragon processors are better.
Display : A AMOLED hd diplay will provide us a better picture clarity. We should also check the resolution of the display inorder to conform the clarity of display.
Camera : Of you are interested in photography its better to check the phones with best camera. Else a 13mp camera is good option. It provides a promising clariry.
Another thing we should confirm is whether the phone is a HYBRID SLOT one or not. Hibrod slot mean we can either put a additional sim or a micro sd card in it. So if we want to use dual sim its better to look for phones without hibrod slot otherwise you cannot insert micro sd card.
Battery : 3000mah batteries a provoding a good backup. Li- polymer batteries will have less weight than li-ion battery.
Its also better to check the review of used ones so we will get a ckear cut idea about the performace.