Is one of these shank styles capable of more heavy duty work or is the shank style the only difference between an SDS MAX and a spline type shank like in a Makita HR4041C rotary hammer.
The shank is is not what makes a good tool.
pwrrrrrrr, BALANCE, Vibration, etc - this is what makes a good tool.
I've never used the HF units, but there seems to be a couple recommendations on that on your other thread.
For budget, look at Bosch. For a bigger budget, go with Hilti.
Again, hammer drills get used HARD.
I'd skip the used market and just look new.....