Get your diet on track first! You'll create your abs in the kitchen dude! Don't worry about cardio, diet first. In my opinion the only need for cardio is stubborn last minute fat loss for a competition or overall general cardiovascular health - shouldn't be your main point of attack to get that six pack. Plus, running can have a lot of issues with leg development hard on your joints etc. hit up an elyptical or stairs. Minimal impact.