SDS, SDS Max, and Spline refer to the type of chuck the tool has. Just like English and Metric the types aren't interchangeable. Generally speaking SDS Max and Spline are found on the bigger rotary hammers and SDS Max has pretty much replaced spline. Some manufacturers even have a "conversion" chuck that allows you to use, say, spline, in an SDS Max tool. That could be useful if you had an assortment of spline bits and buy a new tool.
I'd second the suggestion renting any tool you're considering buying.
