From what I have heard, both ships feel like slight deviations from the Tier 8's before them. That being said, some people prefer the variant type.
I've played the Seattle in Ranked and enjoyed playing here. I don't think I had exceptional results, but I was new to the ship and playstyle, so that's to be expected. The experience was fun, though.
I recall the Buffalo being awkward, but I was extremely new to the game. You do want to get your back guns into the fight in a way that the Des Moines/Baltimore doesn't because of having only one rear turret. That and some other characteristics may feel awkward. Still, she has advanced pen angles on some scary AP shells with a 10km radar and 27mm nose, so she's absolutely worth a try.