I'm generally a flats guy, and I've tried a few. I don't have one set that I swear by.
Dunlops - I have them on my SB-2 currently. Really enjoying them. They do have a good clarity to them for flats. Thinking of putting a set on my L-2000.
GHS Precision Flats - These are currently on my L-1000. Acoustically/unplugged, they seem very dead and I want to take them off. But playing them through an amp, they don't sound that way at all and are very full. Thumpy on the E, but not muddy. As I mentioned, this bass sounds so good with them on. Despite how I feel about them unplugged, I won't take them off because of their tone when amplified. Also had a set on a short scale and thought the E was too thin and weak, but they're rest of the set sounded good.
D'Addario Chromes - I've had sets on an L-1500 and L-2000, and thought they sounded great on each. I have a set on my L-2000 now and they're just not doing it for me. I don't feel like they've gotten past the break-in stage, and I've had them for a while. Chromes to me are normally a very mid-present flat. I had the set on my SB-2 before moving them to the L-2000, and they sounded pretty muddy and indistinct on the SB-2. On the L-2000, they seem a little nasally. It's weird.
Fender 9050 - I've had them on my L-2000 and a few Precision basses. I had one set on my LB-100 for 10 years. Similar to the Chromes, but a little less metallic sounding, I guess. In fact, I think I have a set in a drawer somewhere. I should move those into the L-2000…
Labella LTF - had them on my L-1000, now they're on a Squier P. Sound really good, but a little scooped. Lots of thud with a clear top end. Lighter tension than I prefer, but the Squier needs that.
Labella DTB - had them on my L-2000, where they seemed muddy and indistinct, but they're on my LB-100 now and I really like them there. I've also got these on some Gibson short scales and I really like them on those.
Thomastik Infeld - had them on my L-2000, as well as a few Fenders. I don't get the allure. The E feels fine and almost sounds like a round wound. The G is tight and sounds like a dead flat. The A and D are spaghetti noodles that sound kinda in between. They're not horrible on my fretless (where they are now), but I'm not rushing out to buy another set.
Ernie Ball Group Flats - I had a set of these on a 5-string Jazz. The B was really nice, and the set overall was pretty neutral, not too thumpy, not undefined. A little rough on the surface though, but I'd totally use them again. Never tried them on any G&Ls, though.
My favorite strings with MFD humbuckers have always been DR Fat Beams. A perfect match, in my opinion.
For rounds, yes, I totally agree.