Diep.io vs Starve.io
Diep.io
Diep.io is a fun tank-like IO game where players play as pencil-drawn tanks on a piece of white (and sometimes gridded) paper filled with other hostile tanks as well as a variety of obstacles and Polygons. Shooting at Polygons and other players will earn you points to level up your tank to the next tier, unlocking a wide range of upgrades (or "classes" as the game calls them). At frequent intervals, AI-controlled bosses will be spawned allowing players to work somewhat cooperatively to earn a ton of experience points.Many players are calling out Diep.io as being a clone of the previously popular Tank.io (not sure what happened to Tank.io though), but considering that it's currently the last game standing, I guess it's safe to say that new players will never know about Tank.io but will instead be able to enjoy its legacy through Diep.io.
Starve.io
Starve.io is a unique IO game mainly because it is more of a base-building and survival game rather than just a hack-and-slash arena. In this game, you will need to collect resources and turn them into useful items which will marginally improve your chances of survival. The crafting aspect of the game is very much simplified but it can still take you a while to figure out crucial crafting details like how much resources you need to create a certain item. Also, a quick tip if you will - grab as much food and wood as you can at the get-go.As a survival game, there are several important "meters" that you will need to keep an eye on, such as temperature and hydration. Hunger also something that you will need to frequently deal with, aside from other potentially hostile players as well as other monsters like vampires and zombies if you happen to play its other game modes. There is even a "hunger games" version which frankly feels a lot like a battle royale game.
Unlike many other IO games where players are always pitted against one another, Starve.io is a game in which you can actually choose to coexist with other players rather than just swinging whatever weapon you have in hand at anyone you see... though, many players still do that pretty often, especially those better-equipped ones.