Markley Blue Steels, D'Addario Pro Steels, or La Bella Hard Rockin's Steels have imo been the brightest strings I have played.
Basically, if it has "steels" in the name, it's bright. lol
Hi Beams, imo, aren't super bright. They have a polite brightness that isn't really in your face. Wonderful strings.
Rotosound steels aren't super bright, but they do have a grindy hi-mids thing that no other string has. They do however last the longest of the steel strings, ime.
^This man speaks the truth