Sephora would get higher ratings overall from me. I just enjoy shopping there more. They have more luxury brands, you can test more of the products, you can usually get more interaction and consultation-style help form the sales associates. It's just a nicer store too.
Ulta does have it's plusses though. They do carry some brands I haven't seen at sephora, they have the extended lines of drug store brands, they offer salon services (although I don't use them, the point is it's available which is nice to know), and I think they have a wider product mix, meaning more hair and body stuff and tools, whereas sephora predominantly carries cosmetics and skincare and only a little of the other stuff.
Also Ulta is less than half the driving distance from me as Sephora so I go there more often. If they were both equal distance from me though, I'd choose Sephora over Ulta. Unless it was something minor or from a cheaper brand that I needed.