Construct 2 comes with the Gamepad object, which uses Xbox360 controller assignment. PS3 controllers require a special driver that needs to be downloaded in order to use them on PC. However, not everyone will have a controller for their PC so it's recommended to have keyboard controls to fall back on.
For my game I decided to use the arrow keys and Z, X, and C for the "action" controls. Z being "Hug", X being "Jump", and C being "Give". Up and down allow the player to climb ladders or enter doorways or sit down and so on and so forth. I use Spacebar as a "Pause" key, because of it being sort of separated from the rest of the keys. Z, X, and C are right next to each other and feel quite comfortable to be used in tandem.
My personal suggested assignment would be
Left Arrow : move left
Right Arrow : move right
Down : duck/slide
Z : shoot
X : jump
C : action/block
Having up be the block key doesn't seem to make sense on a relational level. The other arrow keys involve directional controls, whereas blocking is an action.
Grouping it with shoot and jump and action makes more sense. Pairing it up with action would also make sense since I'm guessing the Action control is going to be contextual. Then you can also separate Shoot and Action/Block with the Jump key so that the player doesn't accidentally hit the wrong key and waste ammo or get killed.
Anyway, just my suggestion.