Either Sprinter model is ok, Eco is about 5,000 cheaper as it uses many body parts from Shogun (100cc two stroke). These Shogun parts are also cheap.
But both have exactly the same engine, and I don't think there is any difference in consumption. I bought a used Sprinter in 2007, and even when there were problems with clutch and ring/piston the consumption was still over 50km/l. If the bike is used as a commuter bike, not for racing, it gives much better consumption.
The engine has an un-used mounting space for electric start, but installing one, even by Suzuki, will void the warranty. Some modifacation has to be done.