I am a painter and this is just my own,opinion and what I see having to Do and Re-do exterior doors.

It's not really the door you get it is the way or what finish you put on it that will make it last and withstand the elements and abuse of everyday use.Especially if you have kids.

In my experience either one of these doors would be a good choice.

The Mahogany door will be far superior to the Douglas Fir door.

Mahogany is a dense tropical hardwood that has better rot and insect resistance than Douglas Fir.

Douglas Fir is a softwood with some rot and insect resistance.

Mahogany is a much prettier wood and will serve you much better if you desire a semi-transparant stained appearance.

Typically, however, solid mahogany should cost several times more than a solid doug fir door.

Be sure you are getting solid mahogany and not a laminate for that price.