I have a few questions. Not about seed choice, but seed bed prep. Are these new lawns total new lawn or over seeding old lawn? If new, is everything leveled and smoothed out? Low spots filled in and high spots cut down?
I find that for a completely new lawn, a slit seeder is not the best way to go. You will end up with rows of grass that will take time to fill in, look unsightly, and wide bare spaces, open to weed infestation. The best method, in my opinion, would be to run over the soil North to south-East to west with a Vertical Mower. then broadcast seed and roll it over. This method will give you complete coverage, & an even lawn, with less room for weeds.
Slit seeders are nice for over-seeding an existing lawn.