Depending on your growing situation and it's limits, it's really about what will suit you the best. Autoflowering strains have been typically shown to produce the highest yield when grown under a 24 hour light cycle, as opposed to 21/3 or 18/6. Once the seed is cracked, a timer goes off inside the plant forcing it to flower. Although you can harvest within 40 days from seed to bud, the auto-flowering strains will be comically small, and often nothing to brag about smoke wise. If you have a small set-up, on a tight budget, and/or security concerns, auto flowering would be the way to go. They're also especially good for throwing outside mid-summer to pull in a crop before everyone else and cash out.