Relatively speaking they are a tie, which makes this an interesting question.
I own HS, and have not owned RG, so I could be missing a few good points... But here goes...
4 years is a long time to sit and think how to improve an original design. ((To me, RG is in fact HS2. Getaway would then be HS3))
RG has a more interesting layout -- it has a much more physical system of: habitrails, magnets, and diverters. Several improvements: 1. It turns the weak shot in HS (straight up and back, just left of center) to a legit inner-orbit shot that feeds the orbit and spinner, and earns a free ball. 2. Left outlane doesn't stink like in Firepower forward (a curved wall you can rarely nudge off of). 3. A bank of drops in the middle of the playfield. (proto-type had them down the left bank too !) Also -- a super cool beginning to MB that mimics the real game from real life by unloading all 3 balls at once...
HS has better ramp returns to the PF that do not feed the inlanes directly. That was a downgrade to two spoon-fed inlanes in RG. This makes Rollergames easier, which is not good. I would consider lightning flippers on RG. HS has 3 spinners. Name another game where you can literally have 3 spinners going at once.
HS better theme/sounds/callouts for my tastes.
Theme/sounds/art aside, RG is the best answer to your question, thus it was my vote.