Well... yes, I do have a few;
I've been playing bass since 1968, and for about 98% of the time? Those basses all wore flats, so... I've played a bunch of different ones - in all kinds of scale lengths and gauges. So...
Bright flats? To my ears, the center point of flat wounds tonal range is Fender's 9050L's. Anything else is either brighter - or darker (for want of a better word). The flats I've played that are brighter than the Fenders?
- D'Addario Chromes. The light gauge, long scale Chromes are - IMO - obnoxiously bright ; until they break in. Then, they're just... brighter than I'd like. I had an old, very broken-in salvaged set from a project bass that I put on a new-to-me ASAT Bass a few years ago. I could dial most of the "excess" brightness out of them, so they stayed on the bass until they finally just wouldn't stay in tune - or intonate. I have problems with D'Addario strings that don't count here, so I replaced them with a set of Fender 9050L's - and called it a day... I currently have 2 Birdsong Fusion Basses (a 1 and a 2) that have Chromes on them. Birdsong basses have pickups that are wound for Chromes, so on those two? Chromes are not very bright - at all... I'm liking them - on those basses - so far, so there they will stay. For the foreseeable future...
- EB Slinky Cobalt Flats. They are definitely the brightest flats I've ever used. Chromes can give them a run for their money - for about a week. After they start to break in? The Cobalts stay really bright; the Chromes do not... I have the 45-100 set on a Stirling Sub Ray that I bought a few weeks ago. Aside from being much brighter than I really like? They're nice flats, and being as how the Sub Ray is active? I can throttle down the brightness quite a bit...
- TI Jazz Flats. I'd class the TI's as
just a hair brighter than the Fender 9050Ls. However, that might come down to the bass they're on, or whether you consider the orchestral overtones that TI's are famous for, counts as "brightness". To my ears? Other than those overtones, TIJF's sound an awfully lot like the Fenders... I have a set of the TI's on a bass that does need those overtones, and can take advantage of them. My '95 Alembic Epic, that I use for Jazz. It's also the only bass I own that gets finger-played all the time. I'm so used to playing much stiffer flats with a pick, that my technique just doesn't work with the TI's...
- Dunlop Flats. Well, maybe... The only Dunlops I've played are the short scale ones on my Serek Sacramento, and those don't strike me as very bright at all. Slightly to the dark side of the Fenders, IMO. But, that could just be the short scale thing...
- Roto RS77s. Uh... no. I've had them on a couple basses, and they stayed for a number of years. I'd class them as midway between the Fenders and the heavy gauge La Bella DTF Thump Monsters. Once they're broken in, anyway. Steve Harris' Roto's sound kind of bright because he changes them after every show. They never get to break in... Other flats that are at least midrange-y and mellow? Dogal's JC 106 Jaco Carbonsteels (similar to the Hellborg Flats, but a lot less expensive); Optima 4440 RB Flats, that are clones of the old Rickenbacker's Maxima 4440 Flats; and if you don't mind very light gauge flats? The 39-89ga. La Bella 760FX DTFs, maybe. The ones on my '99 Dano DC59Pro are... sort of on the brighter side. How much of that is the strings, and how much of it is the Dano? Can't say, really. Most definitely not thumpy, though...
Other than that? I couldn't say. TBH, to my ears? The great majority of flats fall on the "Dark Side" of the Fender 9050L's... Some are pretty close, but most flats are not...
As for tape wounds, as some have mentioned? La Bella does make some tapes that are supposed to be fairly bright. I have some, but I've never tried them. Also, I'm not sure if they're just bright, as compared to other maker's tapes; or bright in the absolute sense. Currently, the only tapes I use are Roto's TruBass88m's; and... bright they definitely are not...