Autoflower or Photperiod?

Okay so ive got a grow box and it will only allow my plants to grow 15" its 29" alltogether minus 8" for pots and 6" for light so im either gonna do 12/12 from seed using a photoperiod strain or do an autoflowering strain i really dont know which one to choose :/ i heard autoflowers have become alot more potent recently and yeilds are increasing ive pretty much decided on my 2 strains for the auto - ak47/auto hindu kush and for photoperiod kandy kush so people which one photperiod or autoflower???

if it were me get fem seeds and do 12/12 from seed keeping them real small

Yeh sounds like a plan