The main difference between the Rawlings Pro Line 3 Wheel pitching machine and the other two is ease of use. They all will throw any type of pitch and 2 out of the 3 will throw faster than almost any pitcher anyone is likely to face.
With both the Hack Attack and the ATEC M3, you are going to have to manually adjust the wheel speeds and the angle of the pitching head to throw different types of pitches. Not only does this mean that you have to remember which wheels to put at which speeds and the angle the heads need to be moved to with the Hack Attack and ATEC M3, it takes more time to make those adjustments and those adjustments are blatantly obvious to the hitter as they wait for 30 seconds or more for those adjustments to be made. Simply pushing a button does that automatically with the Rawlings Pro Line 3.
That, alone, should be enough to mark the Pro Line 3 as the clear winner. There are other issues with the other two machines. First, the Hack Attack weighs so much (152 pounds) that it cannot be shipped via anything but non-standard freight carriers, which leave deliveries at the curb, not at the door. It will take much longer to get it and you may not even receive any reliable tracking information on the shipment. Although it is certainly heavier than a Rawlings Pro Line 3, at least the ATEC M3 at 130 pounds can still be shipped via normal shipping companies like FedEx or UPS. The Rawlings Pro Line 3 ships via FedEx.
Additionally, the ATEC M3 and Hack Attack are built as offensive hitting machines only; forget being able to use them for any kind of decent defensive drills. You also need to realize that when you change the pitch type, it obviously changes the location where the ball is going to cross the plate. The Rawlings Pro Line 3 has wheels on both the left and right to adjust the pitch height and left-right direction, something that is not achieved nearly as easily with the M3 or Hack Attack machines.
The Hack Attack only throws up to 80 MPH, so it is a high school machine, at best, and doesn't even meet your needs. While the ATEC M3 leads you to believe it will throw 105 MPH, that is with both wheels at the same speed, which produces a knuckleball. I don't think anyone on the planet wants to face a 105 MPH knuckleball! The M3 and the Pro Line 3 can both realistically throw a 95 MPH fastball.
Really, there is little comparison other than the fact that they all have three wheels. The Rawlings Pro Line 3 is clearly the best pitching machine of the three!