Well, I don't have experience with any Logitech products, but it's true that they have a very good reputation (even better than Microsoft).
However, I have a keyboard-mouse set to recommend, the Microsoft Natural Ergo 7000 (wireless). The keyboard is of the wavy and split type, which I find very helpful, and it has a large soft leather pad, very comfortable for the wrists, as well as 13 customisable quick access keys, a zoom roller and a set of back-forth keys, very useful when browsing the net. Its highligh, in my mind, is an accessory which lifts the front part of the keyboard by about 5 cm, embracing the wrists and bringing the hands to a very natural position, eliminating much of the strain caused by the repetitive activity of typing.
I bought my set about 2 years ago, but it gave me trouble five months later. I contacted MS post-sales assistance in Athens, and as soon as they heard that I was having problems, they asked me for my address and sent me a free replacement set within 3 days (they even paid for delivery). I have been working on this replacement set ever since and everything is just as I want it to be. I know that many people think it is not very comfortable (we had a relevant discussion here at the forum about a year ago), because of its hard and noisy keys (mind me, they are noisy!!!), and also the wrist support accessory isn't very helpful if the user doesn't type in the "blind" system, but it only took me two days to get used to it and I am very satisfied.
The set I am writing about is wireless and quite expensive, but if you don't prefer wireless equipment, you can buy the conventional, wired version of the keyboard (but with a different mouse) and at a much better price.
More info here: http://www.microsoft.com/hardware/mouseandkeyboard/ProductDetails.aspx?pid=095
Καλό Πάσχα και καλή ξεκούραση!