I often paddle with both arms pretty much locked straight.. Both arms.. and through both the power part of the stroke and the recovery part of the stroke.. locking out the arms like this brings in the core muscles more.. and it's both 'push and pull'.. imo.. .. Bending the top arm slightly at the catch part of the stroke will give slightly more reach.

DJ

Yep agree with the other guys. By worrying about whether its punch or pull you will only be using your arms which will quickly wear you out and be very inefficient. Both arms stay fairly straight but relaxed and that way you tend to naturally use a mixture of arms/shoulders/back/core and legs in the paddle stroke. When it clicks it kinda feels like a really nice relaxing rocking motion with your whole body just flowing and you shouldn't feel any real strain on any part of your body at all. Of course when you get out into surf things are gunna change a little when you start taking shorter and sharper strokes to gain quick acceleration to paddle into waves and paddling back out and trying to avoid a belting in the impact zone. Even when you do get out in the surf though, as soon as you are clear of the wave area you should tend to slip back into that comfy technique that you use in the flat because its efficient to cover distance and much easier on the body.