One that's big enough to cuddle us. They also should get along fine in the increasingly small environments we are being shoved into. Having a newly domesticated animal that is limited to the ultra rich with giant estates is pointless, right? Bonus points if we can make it an environmental win as well.
Just about everything 'big' fails at being in an apartment though. Big cats, even the smaller ones among them, need more room. Same with bears, moose (cooool, dudes, am I right? Imagine lounging with a moose), elk, whales, dolphins... bah.
My idea, then? Giant birds. Big enough to lay on you when on the couch, but could be let loose to fly around while you're at work. It would take an incredible amount of domestication to get them to go and come back, but if we're talking hypotheticals and theoreticals and blue fantasy, I think giant birds would be the way to go. Take your pick of them. The steller's sea eagle and especially the phillipine eagle speak to me, but I wouldn't turn my nose up at a swan, a goshawk, or a red kite. Feed them well at home, pretend that during the domestication process we made the nesting area easy to clean, and imagine being able to set it loose on stupid fascist leaders.
