Pros and cons to both, autos can get stuck and flood, and you can't tell how much a horse has drunk, they can also freeze in winter. No carrying of buckets though and very convenient.
I use buckets in my stables (nice heated ones so no frozen water) but my outdoor troughs are mostly automatic.
I prefer buckets indoors, anyway, plumbing everything in my barn for auto waterers would be expensive and our water system wouldn't like it either. Autos outside everytime given the choice, but I keep making new paddocks and can't keep laying new piping to them all.
Buckets indoors are best for the reasons stated above. However I HATE filling water buckets so I could never give up my autos. I love them! Moving to a yard with them was the height of luxury!
Hmmmm, I also have a very playful mare, who empties water buckets for fun, so have a manger at the moment but was thinking of autos as we are having some stables done at home, will keep with the buckets inside and prob try for auto's outside!
Auto's every time.
Fresh water on tap, if well insulated don't freeze, and if you are on a water meter you throw gallons away every day if you use buckets.
Have had them for 20+ years.
Biggest anti for automatics is that you can not tell how much or little a horse is drinking.
I fill my buckets with the hose - much easier than lugging buckets around. They get a scrub out once a week.
We have auto drinkers in both stables and field. Absolute godsend having them inside the stables- they didn't freeze once this winter, and during the snow when the horses were stuck in 24/7 and we couldn't get up to them until early afternoon they always had water.