What is it about flats that interest you? Is it a tactile thing, as in, you like the sound of rounds but would like a smoother string? Or are you also interested in the old-school tone as well?
As others have pointed out, it's hard to give suggestions because a lot of it is suggestive, but:
- If it's option A, look at D'Addario, Ernie Ball, Fender, Dunlops, etc.
- If it's option B, look at La Bella, Pyramid, GHS Precision Flats, etc.
I've tried most flats out there — the only flats I haven't tried on Strings By Mail are the Curt Mangan, Dogal, SIT and the La Bella Olinto — and my advice is:
- Go for the lightest set
- Don't buy the La Bella Low-Tension Flats — the E, A and D strings are probably my favourite old-school sounding flats. The G string does not sound like the rest of the set. It sounds much brighter, and it never settles. Someone took a set apart and found out the G string was constructed differently than the rest of the set.
- La Bella has the worst QC and their customer service is mostly atrocious. My favourite old-school flats are the 760FL (because the G LTF string makes the LTF a no-go), and I love their tapes, but I'm done with La Bella because of QC and customer service.
If I were to buy strings Group A, I would buy Dunlops 40-100 — however, I've had a sort of intonation issue with the G string (see this
thread). I don't know if it's an issue with the 45 G, and I don't recall if I mentioned it in the thread, but when I brought up the issue with Dunlop, they sent me 2 full sets free of charge. Both had the same "issue," though.
My choice for Group B would be the Pyramid.
At the end of the day, though, I wouldn't put too much thought into it besides choosing from group A or B. As others have pointed out, some strings are stiff AF. Others feel like noodles. You'll need to experiment.