FWIW I think the easiest last boss is ingvar on heroic - if you're not mental and avoid all his smashes and roars which are very easy to do you practically dont have to heal.

For first bosses I find the snake boss in gundrak easier than the mammoth (though the mammoth is cake too) - just put your DPS up on the ramp coming in from the entrance to the instance and drop healing stream totems and you don't hardly have to heal or worry about any adds.