I've got a couple links. Let me just leave them here for you.
Let's say, hypothetically, that you have the power to get one of them on his team's Opening Day roster. The other one gets cut. There are no loopholes here; you do not get to not choose and hope they both make it, you do not get to choose someone else (Emmanuel Burriss, come on down!), and I never said anything about a genie, so you certainly do not get to wish for infinite wishes. You choose: one makes the team, and the other one does not.
The question is simple: Which one would be funnier?
Imagine Barry Zito, returned from a year playing guitar and picking avocados, back in the majors. Now imagine that bitter A's fan who thinks the Giants are entirely responsible for the lack of a new stadium, the constant roster turnover, and Mount Davis having to root for him again. Imagine that bitter A's fan painstakingly going through years of comments on the Internet, desperate to remove any traces of his calling Zito a traitor, or saying he'd never be welcome in Oakland again.
Imagine that A's fan, who watched Zito win a Cy Young and become an All-Star with Oakland, having to face the fact that Zito won two rings despite being terrible with the Giants, and grudgingly accepting that this was best for Barry. Imagine that A's fan coming to grips with life in a two-team market, and that the Giants' success doesn't invalidate any of the impressive accomplishments of the A's. Imagine that A's fan realizing that maybe, just maybe, Barry Zito did deserve those rings, and that he should be cheered for all his accomplishments.
Now imagine Zito gives up four runs in his first game and gets DFA'd two days later. Hilarious!
Dan Uggla did nothing right with the Giants. I mean, maybe he was great in the clubhouse, but on the field, he was terrible. But he was the kind of terrible that you could laugh at because not only did he reach the realm of comedy, but it didn't matter! The Giants won the World Series, which makes it even funnier. Not even Dan Uggla playing like Jeff Keppinger lost the defense and unstoppable bat could prevent Even Year Bullshit.
But now come with me, if you will, on a magical voyage through time and space into a land I like to call Whatifopia. Here in Whatifopia, we examine all the possibilities of the world in order to find the most entertaining. And on Isla Uggla in Whatifopia, we've seen the future where Dan Uggla's problems the last two years really were caused by vision issues and a concussion. And in that future, he comes back to absolutely torch the Braves for screwing up the diagnosis and then letting him go. The Braves will make a surprising run at the playoffs, only to be derailed by an early-September series in Washington where, led by American hero Dan Uggla, they get swept, and knocked out of the race. Frank Wren is left bemoaning the Uggla DFA, Chipper Jones admits that no one should ever listen to him, and General Sherman comes back to life and burns down Atlanta again.
Because screw the Braves.
There are a lot of good arguments on both sides, so it looks like I can't settle this with just my words. I have to use the cheapest, most wishy-washy tactic in my arsenal: the poll.