Pendulum squat is way better to me and humbles you better than any hack squat ever could. My gym doesn't have one yet, so my friends and I sometimes drive an hr away to a gym that does have one to use it for leg day.
I would probably get a pendulum. As it seems to be more an over all thigh/hip machine. Where the hack may be better for the quads especially when pushing back against the back pad.
Hack. I personally think the pendulum is overrated because they are less common. Something about the resistance curve to me feels off when you load heavy.
Space wise the hack squat at my gym would fit in a smaller space. I would pick the pendulum squat because for me it "feels" better and for whatever reason, heavy weight doesn't dig into my shoulders. That could partially be because of the pads
Depends on what brands you are comparing...there are certain hacks I would pick over certain pendulums, and visa versa. Most important would be to have used the specific piece before your buy it.
Have you tried one or both? Just look at responses here, very individual. I'd go with what you like and as these are likely big and expensive pieces...maybe drive a bit to try if you haven't ever had access.
Personally, I never cared for the hack machine much but never tried a pendulum. People that I really respect for knowledge of equipment online seem to like the pendulum.
I will also say that if I already had a regular leg press...it could have a big effect on my preference as I'd likely go with this first over either (old school Bodymasters or Nebula being my favs).
I love the pendulum because it's hard as hell but if I was building a home gym and could only choose one or the other it would be a good hack squat machine.
Hack squat. Hack just hits different for me. I always felt like I can overload it a bit more and eek out a few extra reps. Destroys my quads. Is it the best for overall strength compared to back squat, no. However that wasnt the question.
Personally, I know the pendulum works better for me and feels better on my knees. But then again, these long-ass legs give me different leverages and joint/pain challenges than more normally-limbed humans.