It seems the game is optimized for a console. Only advantage of keyboard are the shortcut (Y instead of "3,3" for overwatch for example). [That means, tapping Y instead of tapping 3, because when you tab to other soldier, you cant input a command until previous one finishes) I have an old usb joystick, it seems those are extinct, game options indicate that only 360 joysticks works.
My english writing its a little rusty, i'm sure there will be grammar mistakes. Sorry about it.
its a comfort choice, which ever you find more comfortable. the whole keyboard vs pad issue should only ever be an issue with games that require faster reaction speeds. i don't really need to say which of the 2 is faster and more precise, only an idiot would get it wrong.
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Personally I find that keyboard and mouse can get pretty awkward (especially inside larger UFO's) and that using a controller helps clear that up. However at the end of the day, this game is primarily single player with no demands on reaction times, you won't be finding any situation where one control style will give you an advantage over the other.
Two points of note, if you have your PC hooked up to a TV so you can play from the bed or couch with a controller, the game will still force you to use a key board for any renaming you do. And if you play multiplayer, time limits on your turn may be cause for controller's more streamlined input style to offer an advantage over the clock.
PSN: Lilithian-V- I think anyone who didn't experience gaming on the C64 back in the 80's shouldn't be allowed to professionally review games today. My opinion
KB+M. You can cheat with it. For instance, you can move a sniper forward, make them overwatch with pistol, then re-select them and hit 'X' to make them switch to sniper rifle. Free sniper overwatch. It might be fixed, but for the time being.. yeah.
Keyboard and mouse doesn't really offer any real advantage. The only thing the keyboard and mouse lets you do that you can't with a controller is to zoom the camera in and out freely and to directly select your soldiers or targets by clicking on them.
The controller is just way smoother and makes the game flow better. The mouse controls are waaaay too loose and you spend half your time fighting the map trying to get your cursor where you actually want it. Unless the two things I mentioned are esential to you being able to enjoy the game then I'd recommend a controller.