All carriers with in-house CDL schools suck, right? So, which one SUCKS THE LEAST???

Actually I do not totally agree with that.
Company schools and some of the mill schools will only teach you to pass the test. They will only give you limited driving time and no knowledge of what to do when on the road.

A real truck driving school will go in depth on how to operate on the road.
They will teach map reading (how to do it properly). Route planning. Trip planning, many various backing techniques for many of the backing situations you will get into, and also the reason we do certain things when we are backing a truck or driving a truck around turns forward.

They will also teach how to do a proper pretrip. Not just what area to point in when you say a name you memorized.

Too many of the schools teach you tricks.
For example. They will show you how they want you to set up for an alley dock. Give you fixed points to use so you know when to turn and how much, but they will not teach you why you do this.
So when you get into a situation where you cannot use those marks you will be lost. Or if you do not have the room to set up the way they taught you, you will never get it into the hole.

I could go on for days on this.
All of these necessary things you are supposed to learn are left for a company driver trainer to teach you. But many of those trainers have only been driving a year or less, and they do not even know how to do these things properly. Plus many of the trainers at these company's are broke ### lease Ops that need you for a log book. They do not have a vested interest in you really learning anything.