The two setups don't quite serve the same functions.
The Kelderman is a true air-ride system (at least for the rear) and will give you the best ride.
The Sumo Springs are helper springs, with the benefit of not making the ride stiffer like traditional helper springs, and can help the ride if the coach is so heavy its hitting the stops. Also, the SumoSprings have inherent dampening properties that other springs don't have, which means adding the extra springs does not require upgrading the socks, which can be needed with both helper springs and air-ride systems.
Even the Kelderman system may require shock upgrades, as air springs have no friction at all, so the ride can feel less controlled in some situations (like through drainage dips aka "whoops", or even speed bumps) which could make additional dampening (aka stiffer shocks) desirable.
2000 Ford E450 V10 VAN! 450,000+ miles
2014 ORV really big trailer
2015 Ford Focus ST