1) is the DC 13.4 a good long lasting reliable headset?
2) Are all connections on these headsets standard? i.e will it fit a Cessna in SA, a Rallye in Ireland or an F22 Raptor in Nevada?
To answer your specific questions:
1) Yes (I own two, no problems with either).
2) Essentially yes. The 13.4 is fitted with GA plugs that should work in all civil airplanes. David Clark manufacturers and sells adapters for other uses (e.g., helicopters); see further
here.
Whether DC is 'the best' headset brand is a subjective question, and as
Irishwingz didn't ask it, I won't venture an opinion.