I regularly transfer at AMS, FRA and ZRH. Agreed that ZRH is the easiest. AMS is effectively one very large terminal with a huge amount of walking if you are unlucky. FRA (transferring LH to LH) is pretty easy. You can sometimes get caught out with a long walk, but recent experience is that if the flight into FRA is late they meet you at the door and transfer you directly to the next plane.
A new 748 is likely to be more comfortable than an old 744C.