I ended up putting on DR Lo-Rider nickels and so far am pretty pleased with them.
I love Lo-Riders and when I owned a L2500, it was my string of choice. That said, you might want to give the LaBella flats a little time to break in.
Good choice!
I bought an L-2500 this past spring and the previous owner had TI Jazz Flats on it. I liked the sound of the TI's on my Precision but they they just didn't do it for me on the L-2500 for some reason (maybe too many mids for the strong mids of those beefy MFD pickups?). However, I like a pretty stiff string so no matter how much I like the sound of the TI's on a bass I'd pass on them based on feel. They're WAY too loose for me. But, if you like a flexible string, then they might be worth considering.
I then tried NPR Helix's. I've had them on other basses and liked them a lot but on the L-2500 I wasn't crazy about them. I think part of the reason was that I bought a lighter gauge string than I'm used to and that produced too much rattle and clank with my heavy handed, Neanderthal technique. However, I did like the ones I had on my Stingray and I'm now on my second set on my FrankenJazz. Nice sounding strings.
But then I tried my favorites, Nickel Lo Riders, and even after being on the bass for a few months, they still sound fantastic to me. No surprise though. I've had Nickel Lo Riders on most of my basses at one point or another and I haven't had a bass that didn't sound great with them.
That being said, I at one point considered trying Sadowsky Black Label Flats or LaBella DTF's to try try taming the bass to some extent (maybe a little with the Sadowsky's or a lot with the LaBella's) and bought a set of both. I ended up putting the LaBellas on a different bass (on my Precision V - WOW!) but the Sadowsky's remain unused for now. I'll probably try them next on the L-2500 after these Lo Riders finally wear out but, for now, the Lo Riders sound great on it!