Not just parroting, but based on my experience, you'll not find another second stage that breathes noticeably better than a well tuned updated G250, different breathing characteristics but not "better".
First stage, they all do the same job, for rec diving anyway, assuming balanced, performance is all but in the second stage.
Is there something you don't like or find lacking with your G250?
Pistons for the MK10 are almost impossible to find new now and have been NLA for many years.
Basically buy the reg that takes your fancy, one that you can get serviced relatively easily and meets your diving requirements, cold water etc etc.
Shopping is fun.
If you're hell bent on buying a new reg set you'll not go wrong with either AL or SP. the MK17 can have a substantial ip swing which irritates me a little. If
@axxel57 says the legend has the lowest ip swing of any first stage he's tested then it is so, but boy are they big first stages.
Personally new, I'd go a G260 with an Apeks FSR first stage. If you don't want to mix and match brands, which "can" complicate servicing, get the legend.
Currently SP do not offer the MK19, apparently only a small ip swing, as a set with the G260 only in black tech/carbon which is a pretty penny.
Have fun, good luck.