I played with a blind pianist who said the more sharps or flats, the better, because he could feel the keys better.
Because I come across these keys so infrequently, anything with a double sharp or double flat would be a cause for a slight pause if sight-reading.
Matt, when modulating a half step up from C I think C#, but if reading I'd choose Db. And for me F# is definitely easier to read than Gb -- all those years playing with guitarists who like E did that for me.
To get back on topic, I think if anyone feels that flat keys sound duller than sharp keys or sharp keys sound brighter than flat keys, it's a preconceived notion and their brain makes it so.
But then again, perhaps it's my brain that refuses to accept such a notion

Insights and incites by Notes