The one reason people always use in the argument of which is better, PC or consoles, is that consoles can have split-screen play
Where you can play on 1 copy of the game with a couple of your friends in the same room
I cant really argue against people that use that reason as PC games normally dont have that feature, and it is a good feature to have

But Portal 2 for PC has this feature, unfortunately its not advertised or even really supported
Which is a shame because more games (for PC and consoles, but mainly PCs) should have this

How to play Portal 2 Co-op in split-screen mode on PC (and MAC)
Set 1:

1. Enable the dev console by going to options, keyboard/mouse and switch Developers Console to Enabled
2. Open the dev console by hitting ` (the key to the left of 1, and above Tab)
3. Type "ss_enable 1" without the quotes, and hit enter, this will enable split-screen mode
4. Close the dev console and click Play Co-op from the main menu, wait for it to load the friends list
5. Open the dev console again and type "ss_map mp_coop_start" without the quotes and hit enter, this will load up the very first map to start playing on

From there you can play through the game without needing the console ever again unless you want to stop playing
If you want to stop playing just exit like normal and the next time you want to play do step 2, 3, 4, and 5 again
But for step 5 use "ss_map mp_coop_lobby_2" instead
Youll also have to do steps 5 and 6 from Set 2 (see below) again

Now you may have noticed that the 2nd player cant do anything
Thats because you need a controller for the 2nd player
The controller needs to be set-up before you start portal 2

How to set up a controller (for PC only)
Set 2:

1. Go to Program Files\Steam\steamapps\common\portal 2\portal2\cfg
2. Copy joy_configuration.cfg and paste it into the same folder, rename it to joy_config2.cfg
3. Open joy_config2.cfg with notepad and add cmd2 in front of every line, or just erase everything and paste this into it:

Code:

cmd2 joy_name "Xbox360 controller" cmd2 joy_advanced 1 cmd2 joy_advaxisx 3 cmd2 joy_advaxisy 1 cmd2 joy_advaxisz 0 cmd2 joy_advaxisr 2 cmd2 joy_advaxisu 4 cmd2 joy_advaxisv 0 cmd2 joy_forwardsensitivity -1 cmd2 joy_sidesensitivity 1 cmd2 joy_pitchsensitivity 0.75 cmd2 joy_pitchsensitivity_default 0.75 cmd2 joy_yawsensitivity -1.5 cmd2 joy_yawsensitivity_default -1.5 cmd2 joy_autoaimdampenrange 0.85 cmd2 joy_autoaimdampen 0.5 cmd2 joy_lowend 0.75 cmd2 joy_lowmap 0.25 cmd2 joy_no_accel_scale 1 cmd2 joy_accelscale 2.0 cmd2 joy_accelmax 1.0 cmd2 joy_response_move 5 cmd2 joy_response_look 1 cmd2 joyadvancedupdate cmd2 crosshair 1 cmd2 hud_draw_fixed_reticle 1 cmd2 bind "JOY1" "+jump"         // (A) Button cmd2 bind "JOY2" "+duck"         // (B) Button cmd2 bind "JOY3" "+use"            // (X) Button cmd2 bind "JOY4" "+remote_view"         // (Y) Button cmd2 bind "JOY5" "+quick_ping"         // Left Bumper cmd2 bind "JOY6" "+zoom"         // Right Bumper cmd2 unbind "JOY7" //"+mouse_menu_taunt"   // Back ("select") Button cmd2 bind "JOY8" "gameui_activate"      // Start Button cmd2 unbind "JOY9" //"+quick_ping"      // Left Stick In cmd2 unbind "JOY10" //"+zoom"         // Right Stick In cmd2 unbind "JOY11" cmd2 unbind "JOY12" cmd2 bind "Z AXIS POS" "+attack2"      // Left Trigger cmd2 bind "Z AXIS NEG" "+attack"      // Right Trigger cmd2 bind "POV_UP" "+mouse_menu_taunt"      // D-Pad cmd2 bind "POV_LEFT" "+mouse_menu"      // D-Pad cmd2 unbind "POV_RIGHT" //"+mouse_menu"      // D-Pad cmd2 unbind "POV_DOWN" //"+mouse_menu_taunt"   // D-Pad cmd2 joystick 1 cmd2 sk_autoaim_mode 2 cmd2 +jlook

4. Plug in the controller, start up Portal 2, do steps 1-5 of the other steps in Set 1 (see above) (step 1 of those steps only needs to be done once, so ignore it if you already enabled the dev console)
5. After the other step 5 from Set 1, while the map is loading, unplug the controller and plug it back in
6. Once the map is loaded open the dev console and type exec joy_config2.cfg

And then you should be able to play with player 2 being able to control his player with the controller
Player 1 controls his player with the keyboard and mouse, like normal

Ive only tested this with 1 controler, a wired 360 controler

Yeah, its best to play with someone else that hasnt played co-op on your first play through, so that you can really work together to solve the stuff