Both machines are very similar in their basic components, features and dimensions.
Scag Liberty features;
5.5 gallon fuel capacity.
New model Kohler 7000 series engines, not much known about them.
48" and 52" decks available.
Separate parking brake.
A good selection of accessories/attachments available.
Although the Liberty Z is new in the Scag line, it is a spinoff of the Freedom Z line.
Hustler Raptor SD features;
3 gallon fuel capacity.
Kawasaki FR series engine, been around for a long time.
48", 52" and 60" decks available.
Patented parking brake system, nice feature!
A good selection of accessories/attachments available.
The Raptor line has been out for a while and many have been sold.
Hustler is coming out with a flip up deck model fairly soon, you might consider it!
At this point, fuel capacity, engine choice, parking brake and dealer comparison are your main concerns, your decision!!!