While both have their perks, the idea of being able to change your physical form appeals to me more.
WHO WOULDN' WHANT TO TURN INTO AN ANIMAL
You can change into anything!
It's pretty much a free pass to commit any crime you like. "Who shot that man?" "A bald, black man of about 6 feet tall" "Any luck finding him?" "No" "Well, that's unfortunate," says the 5 foot tall, white women with long flowing hair.
A metamorphagus can transform into anything they wish whereas an animagus can only transform into one animal.