If you have been running enough in the ASICS that you've worn a hole in them, perhaps buy the newest model of those shoes as a replacement as they seem to suit you?
Broadly running shoes are either designed to be stabilizing/supporting or cushioning as one pair can't do both things perfectly.
Gait analysis at a running shop will give you an idea if you tend to roll inwards, which would call for stabilizing ones or not. Cushioning ones are more springy and are supposed to protect the joints from the shock of running more.
First of, if you are training for a marathon, I assume its road running, and therefore discount any that say 'trail'. Secondly, decide how much stabilizing or cushioning you need.
I personally think two pairs of slightly cheaper different trainers is a better bet than one pair of hugely expensive ones. As each shoe gets a chance to recover between uses (and dry out if necessary) and they tend to correct the gait problems caused by the other, if that makes sense.
I would go to a running shop to buy a pair if you are really not sure, but after that, if you know what you like, its often much cheaper to buy last seasons colours (I tend to buy from here ).
Good luck for you Marathon! And buy some good socks, they are half the battle!