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I personally prefer DRS over all of them, but each of them is horrible by itself, and better when viewed together. Each should be viewed, and each should be taken with a grain of salt, because none of them are perfect. Each has flaws, but you will at least get a decent idea if you view each of the three. I personally think each defensive metric should be used as a round number, and not a specific number. I.e. if a guy is saved to have saved 13 runs defensively. I would say it would be safe to say he saved between 10 and 16. Or for UZR, if a guy is a -3.3 UZR. Then he is probably average to slightly below average.
What part-timer were you comparing to a full-timer? There are a lot of ways to break it down. It just depends the size of the sample size really.
You can use rWAR and divide by PA to get a WAR per PA for a part timer vs a regular if you would like. But WAR wouldn't be a good enough sample size probably to compare two players. Assuming you are talking about in an individual season.
For defense, I would look at three different stats
Baseball-Reference has Total Zone (TZ), which is a good snap shot
And then Fangraphs has two stats
UZR and/or UZR/150, which is what they classify under 'fielding' when you look at the players home page.
And Defensive Runs Saved (or DRS) which is further down under Advanced Fielding.
(have to break into two postings)
Baseball-Reference, Game Logs, top of the page (I sent in another message, did it not go through?)
Most Driven In: Self 44, A Jackson 38, Q Berry 13, A Dirks 12, O Infante 8, B Boesch 7, G Laird 5, R Santiago 3, ...
He drove in Austin Jackson 38 times (most he drove in of anybody).
If you go into Baseball-Reference, under Game Logs (it should highlight) and then you can select 2012. It's in there under information before the first game
Victor Martinez = God
∞ times ∞