With the exceptions of
Blanche and its variants,
Blossom, and
Blodwen, I think
Bl- names all sound rather masculine.
Blake,
Blair, etc all sound 100% male to me. That view is heightened by their surnameyness for me.
So I much prefer
Blair on a boy only. I prefer, regardless, the spelling Blaire though (in contrast to my usual preference of original spellings). Blaire just looks more complete to me.
Miranda