I've had all three. Birds are the easiest, but also the loudest.
Dogs need a lot of room and attention. They eat a lot of food, take big stuffs, need a lot of loving shots and are generally nuisance, even if they show that much love to you. Cats love to scratch everything, disappear into the loving void, are way more temperamental and overall just plain old richardheads.
But birds, man. They're loving idiots. They'll eat literally anything, they're happy to stay in their cage, they really only need attention once every 2 weeks (to clean the cage, replace food/water, give them that vitamin stuff) and they stay out of their way. Besides, they're hella more loving entertaining when you watch them. Also, some birds can be taught to be speak...works great if you swear a lot.