I've recently went between two different sets of RotoSound strings; RS66LC (40, 60, 75, 95) round wounds and SM77 flats (40, 60, 80, 100). The two could not be more different from the point of stiffness. The RS66's are rather floppy, far more than I like (my right hand can get a bit heavy). The SM77's are very stiff. Strings that you can really dig on with the right hand and set up beautifully if you like looowwww action. Unfortunately, the SM77's are very thuddy and the E string went somewhat dead down low (G and lower) in just a few weeks.
Currently, I am playing D'Addario XL Chromes super lights (40, 60, 75, 95) and they are a good balance between the two RotoSound sets; stiffer feeling than the RS66's but not quite as stiff as the SM77's. Action follows suit, higher than the SM77's but lower than the RS66's. Notably more definition, brightness, and punch than RotoSound flats.