I stopped counting the number of auto strains I've grown.... but it's a lot. But the phrase "fast auto" will certainly have different meanings to different people. How fast are you looking for?
In my experience Royal Jack Auto is a 12 - 14 week, seed to harvest plant - running 24/0 under 400 watts (LEDs). This one was a consistent semi-predictable plant.
I've never grown a "fast one" but I've done a "quick one" and it's a 10 - 14 week, seed to harvest plant - running 24/0 under 400 watts (LEDs). This one I found to be a lot more unpredictable on its grow time.
Now both of those "could" be harvested sooner, but my harvest time frame is based on when it's actually ready to harvest for best yields. Also, I've ran both of those plants under a 600 watt LED setup and had similar results - nothing substantially better that would make the extra power burn worth the cost. I generally test plants under different setups to get a better understanding of the strain.
And my "watts" rating is actual power consumption - not any of the crazy "its just like 3000W" nonsense that is common with LEDs today.
So, overall, there are certainly faster strains to grow. Some of the older less popular strains like Lowryder have been pretty hard to beat for "fast" strains. Lowryder is a solid 8 week, seed to harvest plant - running 24/0 under 400 watts (LEDs). But it's also not the best on the 'yield' front.
And some of the Fast Buds strains are pretty fast as well. Just depends on what you are looking for... would need more information about expected time frame that is "fast" and yield amount to give a better answer.
gyo.green
and
attitude seed bank
Both are reliable seed banks.