depends on how you look at it - like as a full label, crew - i'd go no limit. that tank certified and got play for so many artists who otherwise would not have made any sort of impact.
cash money started of strong as a crew from 98/99 (nationally) to about 01, but pretty much after that, the artist (wayne) kept the label name alive more than the label kept artists alive. i personally don't even think of cash money when i think about drake or nicki, and can't even name artists from the label post wayne/baby that aren't nicki and drake. whereas i dont think mystikal, P, silk, c murder, feind, mercedes, i'm bout it, i got the hook up, mia x, kane and abel, sonz of funk, mr serv on, etc without thinking no limit...so many of those artists i just named are forgettable, but the tank engraved their names in my head more than cash money did for their artists.
and yea, no limit also opened up the "real" south in a way rap a lot and organized noize/laface didn't (their artists had a more well rounded sound) and no limit hit levels of success other "real" southern artists at the time had yet to achieve (UGK, 8ball & MJG/Suave House). i'd definitely say No Limit had the bigger impact, while Cash Money has clearly had the longer run.