The advantage of buying from a pilot shop is that you can try a set on and make sure they are comfortable, and seal well (preferably trying with the sunglasses you wear). Not all headsets fit all heads very well - not implying you have an oddly shaped head
.
Otherwise, shop around on-line. David Clark have a long track record, but there are other reputable makes (e.g. Sennheiser) which give 10 year guarantees.
If you really want to splash out on a headset for life, have a look at the Lightspeed Zulu.