Depends on who the two players are. A young Donavan Tate who went In the top 5 picks, a young Bubba Starling or a much older Buster Posey or a much older Pedroia. Who had the most upside?
IMO, all things being equal simply doesn't exist. Problem is it is difficult to know for sure who will end up being the best. Being one year younger can be an advantage, then again sometimes maturity can actually be an advantage.
If one year made that much difference the entire first round would be high school kids every year. Why do they draft so many in the first round that are, not one year, but three or four years older? If only it were easy to know which player, one year apart, has the most upside
Well, for one thing it has to do with timelines of player development. If a high school player is drafted in a high spot, say first two/three rounds, and after 2-3 years of development doesn't seem to be panning out, it would seem logical (in a production sense) that you need to replace that player in the pipeline with someone who can essentially pick up where he is leaving off. Therefore it could be conjectured that a college player being drafted in a high round is being drafted not only because that is where they fall on the board skill-wise, but also need wise. It's a machine, professional baseball, with a continuous chain of players driving its gears. If a link in that chain is missing or projecting to jam the gear it needs to be replaced. That's one way of looking at why college players are drafted high.