I haven't had Nuun recently but I've had good luck with Louis Garneau LG1, eLoad and EFS. I think the real key to preventing cramps for me is taking 2 Saltstick tabs or S-Caps every 30-60 mins. Ever since I started using electrolyte tablets to supplement my drinks, I've either prevented having cramps or stopped them from continuing mid-ride.
I use Osmo singles for my during-ride refills. I'll try Nuun again after my stash runs out.