Oddly enough, interceptions are the easiest to do efficiently despite using the most energy. Using this method you should be able to do 21 per match, despite the occasional mess up.
First and foremost you'll want to do these achievements last, simply because there's a chance you'll obtain some via story and hero mode respectively. This isn't required, however and can be done fairly early in the game. If you have any skills from hero mode that bolster health or any kind of defense, I suggest you use them. I used Health +1 and Kongo, though for this it didn't matter too much. Here's how I set it up....
1 player match
1P vs 2P
P1 Super Saiyan 4 Gogeta (I don't think this matters much)
P2 Kid Gohan (The only part that matters about this is his energy blast barrage super).
Alright! First and foremost is your method of bolstering the spirit gauge. At first, I thought strong attacks were the fastest way like many of the solutions above but that's not the case. Thanks to admeister over on ps3trophies.org, I learned that charged Ki blasts (hold triangle) actually charge one whole bar per use. This means that after four charged Ki blasts, my second controller was clear to use a super and my main only took 2400 damage. While firing blasts with the second controller I would hold down on the d-pad with P1 in order to boost my ki, especially since each hit drains you a bit. Once your spirit meter and Ki are where they should be, use the super by flicking up on the right stick.
Once the super is coming towards you, wait for the prompt and press triangle. When the clash starts, instead of mashing like it prompts you to simply wait it out. Since this will result in a draw, the attacks will cancel each other and you'll be able to use more attacks per match. Thankfully, you don't have to win the defenses in order to earn these.