Arcticman,
First welcome to the board!
What bow set-up will you be shooting??.....#, speed etc.?
Although I've never hunted either <img src=icon_smile_sad.gif border=0 align=middle> I think it's safe to say that you'll want a quality "Cut on Contact"(Magnus etc.) or Fixed Replaceable broadhead (Muzzy etc.)attached to a pretty heavy arrow. Me personally.....I'd be at or above 500 grains for moose.
Don't even look at the rack of Mechanical heads!
Caribou......you could probably get away with whatever you'd use for deer.....they aren't huge and any quality fixed blade head (Muzzy etc.) on a mid weight arrow (400+ grs.)should suffice ......Mechanicals are a possibilty depending upon your arrow energy.....If you decide to go this route, the Rocky Mt Archery "Snyper" would be a great choice, as would Rocket Aerohead's "Steelhead" . Both penetrate as well as fixed heads and open quickly and using little energy to do so.
In either case make sure that they are SHAVING sharp......and as always, put em' where they count!