I use Rotosound RS66LC's on all my basses except the Spyder and the Exploiter. On the Spyder, I'm currently using GHS Boomers, extra long scale, .40-.95, and on my Exploiter, I use RS66M (medium scale, .40-95). I use the GHS on the Spyder because that's what they have at Guitar Center, but I'm going to go on the web and order some RS66's for my Spyder through Just Strings.
I've used Rotosounds since I've been playing (over 27 years). There was time that I used DRs (mainly because that's what was available), and they're good strings as well. I prefer Rotosound, however, since I'm a big John Entwistle, Chris Squire, Geddy Lee, Greg Lake, etc. fan, and I need that kind of sound. I've found that the Rotosounds give that to me reliably.
I like the lighter gauge strings. Standard gauge strings seem like telephone poles to me, but hey, to each his own. The lighter gauge allows me to bend the string easier, makes popping and slapping easier, and are just better for me when playing a four set gig.
Alan