I am not sure about others but in last 3 months i travelled twice to uae. 1st i got visa on arrival at dxb terminal 1. 2nd time i went by road in my car, i did get visa on arrival at ghuwefat uae border but the captain said this is the last time we are giving you visa on arrival, next time plz apply online. Also i did hear him saying the same to others... i told the captain that i did apply online but it was taking time thats why j could not wait. He said apply 2 weeks before your travel date :(
Anyway eventually they gave the visa but wd lil gir gir gir... :)
My advice, apply online before you go. Else do whatever you feel like :)