We only have about 1 or 2 degrees of 'declination' here, so it hardly matters. Unless dealing with aviation winds aloft reports & charts I'd have to go with magnetic. Also most weather sites give more of a general wind direction anyway. I fine tune the info with local indicators, chimneys & wind on the cheeks, etc..
When setting up to hunt, wind direction is about the 1st thing I consider & adjust accordingly.
I use a cheap but effective wind checker - my wife gave me a leftover squeeze bottle from some girlie/makeup product and I washed it out good and filled it with cornstarch. A quick puff on the bottle gives a scent free indicator that is easily seen. Lasts all season and fits in a vest pocket.