Breaking down the men to top 5, it would be:
Hartman - the perfect super-connector for a sketch show with the ability to play all levels of parts, along with impressions and characters. not always the funniest on his own, but certainly could be and the ultimate facilitator for this kind of comedy. kind of the tom brady or joe montana of the cast.
Hader - similar to Hartman, but a better impressionist and had a higher individual ceiling. maybe the peyton manning.
Farley - highest absolute ceiling. if you want someone you know can absolutely destroy, but is also flawed and not totally well-rounded, he is your guy. the brett favre.
Myers - Could think and write on so many different levels, really a creative genius and excellent performer. the steve young or john elway.
Carvey - similar to myers but a little less on the writing and more on the perfomer. as present and in the moment as performer since robin williams. the aaron rodgers.
So it really depends on what you need and want. I feel like I would go with Carvey personally, but Hartman would be a close second and some days probably number 1 for me.