It is overrated but I actually prefer it to Burger King and KFC. They tend to be the big three anyway. BK is expensive and even though the burgers do taste more real, I still prefer McDs ones. Plus BK chips are awful. KFC is ok, and I tend to go there if I have to choose between the two, but McDs always post really cheap vouchers through my door, hence they win.
Haven't been to subway after I bought a ham sub, put it in the fridge overnight and it was mouldy the following morning. Plus it is overpriced for a sandwich anyway.
I think it is overrated though. I don't like it as much as a lot of people and would much rather go for a pub lunch, considering you can get them the same price as a fast food meal these days anyway.