Get the biggest size screen you can afford, you won't regret it! When it comes to games the more you can see the better, afterall you don't want to be sitting infront of it squinting all the time lol.
A 26" would suffice i'm sure but i'm absolutely certain that you would regret not buying the larger screen, the big question is how far away will you be sitting from the screen? If you are going to be quite close then a 26" may just suit otherwise it's the 32" for sure.