If the slop was wery low, and I was to use a standard can,
my preference would be to used the recessed eyball trim.
I just don't like the eyes that hang below the ceiling, especially on sloped ceilings.
I think that the slope cans and associated trim are more expensive than a regular can with an eyeball trim. That said, I generally give the customer the option if it seems like they might want some input into that decision.
I always use slope cans on a slope ceiling if I can. I think they look better.
However, I think lightolier slope cans are designed for a 4:12 pitch or greater. I recently wired an addition with 3:12 pitch ceiling and used regular cans. Easy to check the pitch.