I am using Microsoft phone since over 2 years and recently bought Lumia 540 for myself and wife.I can confidently say that this phone is best phone in sub 20k category.
My internet usage is quite high but then also battery lasts for about 2 days when fully charged.Camera is quite good and with 5mp front cam you wont get disappointed while taking selfies.
Absolutely no lag in any application but the best deal is personal assistant Cortena. This is going to be a big game changer in near future.
Overall I will suggest this as best buy.