While Cowan is listed among the families associated with Clan MacDougall, Cowden is not (https://macdougall.org/2014/02/16/clan-names/), though it could be down to a variation in spelling.

I’m sure that if you’re inclined to consider yourself a MacDougall, they’d be happy to have you.

The MacDougalls, like many others, had their issues with the Campbells (see Battle of the Red Ford, 1294).

While I have many MacDougall ancestors, there are Colquhouns I hold in high regard, so you’re unlikely to go far wrong either way, IMHO. 😊

Without additional information about the location of your forebears, it may come down to your preference in tartans... do you prefer red (MacDougall) or blue/green (Colquhoun)?

Cheers,

SM