It depends on how steep it is. Either way, I'd prefer an older model. In the newer models, the transmission is crap, which is exacerbated by hills.
These are the top models and choices for anyone looking for an amazing mower for a hilly backyard.
I don't have any experience with Spartan RZ-HD 61" but I've used the Husqvarna mz61 for a long time and still working very well.
Here i found an review on that lawn mower you can check.