IMHO...

1. The Aircore is 100 times more durable.

2. To a newbie, the PT-40 will be slightly "easier", but that doesn't mean you'll learn any faster.

3. Neither is "better".

Some other differences:

The Aircore is a kit. It builds faster than a balsa plane, but it's not an ARF (I'm not sure if you're talking about the PT-40 ARF or kit). If you're thinking of building the PT-40 kit, the Aircore will build much faster.
The Aircore needs a ball-bearing .46, the PT can probably fly fine with an inexpensive .40.
Some people don't like the Aircore, saying it's heavy and sluggish (it is, but that can be a good thing for a trainer). If your instructor is one of these folks, the PT-40 would be a better choice.