When I went over the few positional battles that will be going on during the Spring, the only real battle as far as the starting lineup was concerned was at third base. Brendan Harris is likely to be used almost exclusively at third this year after spending the last two seasons being more of a utility man, and we all know how much Gardy loves him some Nick Punto. I don't think Danny Valencia has any real chance to win the third base job, and since I'm not all that high on him to begin with, I agree that there's no reason to lose someone to waivers (which they'd have to do to promote Valencia) when his production won't be a whole lot better if at all better than Punto or Harris.
Now, while I did say it would be a Spring battle for the starting job, that seems pretty silly. Both Harris and Punto have enough major league at bats where we should be able to predict, at least somewhere in the ballpark, the numbers each would be likely to put up. Defense will be a factor as well, especially if the offensive numbers are relatively close.
Nick Punto seems to be the one most people expect to win the job because of how often Gardy has played him over the last few years, and Gardy was quoted a few days ago saying he "just likes to have Nicky in the lineup" one way or another. Punto is a career .248/.322/.324 hitter, which is well below average for a middle infielder, and downright awful for a third baseman. His on-base percentage over the last four years has been considerably higher than .322 in three of those four seasons though, so if I were to venture a conservative estimate on Punto's line next year I'd put it at .250/.335/.325, which is still atrocious for a third baseman. The fact that the Twins are paying Punto $4MM to put up that offensive line is a disgrace, especially when even half a season of Joe Crede at half that money would likely be an upgrade.
Defensively, Punto has played 224 games over the last four years at third base, so that should be a large enough sample size to get some solid defensive information as well. Over those four seasons, adjusting for 150 games played, Punto has put up UZR's of 17.4, 23.8, 22.6 and 39.1, although the last two years he's played a total of seventeen games at third so that 39.1 is almost certainly more of a fluke than suddenly getting even better defensively. If Punto is a +17 UZR defensive third baseman, that basically offsets his terrible offensive production, and hitting 9th a .335 on base percentage isn't the end of the world.
Brendan Harris, on the other hand, is a career .267/.324/.396 hitter in basically three full seasons. His offense has been about 15% better than Punto's over their careers, but unfortunately for Harris he's seen his slash line decline each of these three seasons. Now, even if Harris matches his weak offensive numbers from last year (.261/.310/.362) he'd likely still be a better offensive option than Punto. I think a safe bet for Harris this coming season would be a .265/.320/.380 line, which is just under 10% better offensively than my prediction for Punto.
Unfortunately, for the slight improvement Harris brings offensively, he gives away more defensively. Harris has only played 82 games at third base over the last three seasons, so the sample size is admittedly small, but he's shown little reason to suggest he's going to be a positive defensive player at any point in his career. Over the last three seasons, Harris has posted UZR/150's of -25.6, -5.9 and -26.3. He played 44 of those 82 games last year, and 78 of those 82 games in the last two years. The difference between -6 and -26 is obviously rather large, and a bigger sample size this season would hopefully be able to figure out exactly just how poor of a defender Harris is, but a conservative prediction in my opinion would be that Harris would post a -10 UZR/150 if given most of the playing time.
Harris would ultimately have to be 27 runs better than Nick Punto offensively to make up for his defensive shortcomings, and I just don't see that happening. Many fans continue to roll their eyes when Gardenhire speaks glowingly about Nick Punto, and rightfully so, because even when factoring in defense Punto is still a well-below average third baseman. However, at this point in their careers, Punto is simply the better option to be given most of the playing time. A platoon would make little sense, because Punto is equally inadequate against both righties and lefties, although Harris is a much better hitter against lefties than righties.
Hopefully when Gardy decides to give Punto/Hardy/Hudson a day off, he chooses to do it against left-handed pitching, because that would give Harris the best chance to succeed and would give the Twins much less of a downgrade than if Harris were to get a start against a right handed pitcher. Most fans assume Punto will win the job simply because Gardy loves him, and while that is likely true, the fact is Punto is the better choice between the two and for once, Gardy's affection towards a player may actually improve the club.