So I thought that, in the absence of some really compelling and timely topic for today, I'd go ahead and post my (slightly modified) ballot here, with comments (and stats from their time with the Dome-era Twins only). This is much longer than I was anticipating and I'm suddenly swamped with work, so we'll stick with the infielders today and pick up with the outfielders and pitchers in separate posts sometime in the next few days.
Catcher: Joe Mauer (.317/.399/.457, 31.6 Wins Above Replacement Player [WARP3]).
He's played only four mostly-full seasons in the Majors, and yet this is the easiest pick until we get to the man pictured in my avatar. Not since Carew, at least, have the Twins ever had a position player that you could really argue was the single best player in the American League...but Mauer is that. Catchers just don't hit and get on base the way Mauer does, at least not the ones who can really catch. I don't know how much longer he can keep it up as a catcher, but enjoy it while he does.
Runner-up: Brian Harper (.305/.339/.428, 16.8 WARP3). No patience or defense, and not much power, but if you're in the just-pre-Juiced Ball era and can find a durable catcher who can hit .300 with 10+ homers every year, hang on to that guy.
First Base: Kent Hrbek (.282/.367/.481, 53.9)
I assume that Justin Morneau is going to win the fan vote, and quite easily, but it should be a blowout in the other direction. Hrbek, a local Minneapolis boy, had more than twice the number of PA Morneau has had so far with the Twins, was a better hitter when you adjust for the difference in eras (128 OPS+ to 122), and was a better defender (both have/had very good defensive reputations among Twins fans, but Hrbek actually earned his). And then of course there were the two World Series. Hrbek never had a year in which his raw numbers looked as huge and pretty as Morneau's '06, but he had several years that, viewed in the proper context, were just as good or better. Morneau has a long way to go. If you're unfamiliar with the story that goes along with the picture to the right, that's Hrbek tackling Ron Gant to make him fall off of first base in the 1991 World Series. And Gant was called out. That performance alone might have been enough to put Hrbek on the top of my list.
Runner-up: Morneau (.282/.348/.499, 21.7), of course. Though I'm more interested in the fact that Ron Coomer (now one of the Twins' broadcast analysts, seen here in Fort Myers in March, photo by the author) made the list. We used to call him Fred Flintstone, for obvious reasons. Seems like a good guy; 87 OPS+. On the occasion he was even the best 1B on his own team, that was a sad team.
Second Base: Chuck Knoblauch (.304/.391/.416, 46.3).
He's become kind of a joke because of his throwing troubles once he hit New York and connection to the Mitchell Report, but when he left Minnesota, Knoblauch looked like a tiny, troll-like, obnoxious, future Hall of Famer. He was an excellent hitter and baserunner, and only the presence of real future Hall of Famer Roberto Alomar kept him from winning, and deserving, a whole bunch of Gold Gloves (he did get one, in 1997). Second basemen as a whole burn out bizarrely early, and that's something I'll explore here someday; it was more in Knobby's head than his body, but he was done as a useful player by age 31.
Runner-Up: Todd Walker (.288/.344/.419, 3) was a fine hitter who was mistreated by manager Tom Kelly, but I was a little hasty in guaranteeing upon his 1996 callup that he'd be a Hall of Famer someday (hey, those were desperate times). John Castino was probably a better player, but only played parts of two years in the Dome.
Third Base: Corey Koskie (.280/.373/.463, 33.7)
Toughest choice of them all. Gaetti had a longer career, even just considering his time with the Twins, and was a better defender. But Koskie was a fine glovesman himself, and was often the one truly excellent hitter on contending teams that really needed help to score runs.
Runner-Up: Gary Gaetti (.256/.307/.437, 28.8). My first favorite player. His hitting was overrated because of his aversion to taking a walk, and he was a little injury-prone, but the power + Gold Glove defense combination was awfully valuable. He's probably become underrated now, as memories have faded and people have started to better grasp the importance of OBP. The Rat also has easily the best and weirdest unofficial fan club on the 'Net.
Shortstop: Greg Gagne (.249/.292/385, 21.2)
Slim pickins here. Gagne was never on base, but was a very solid defensive shortstop with some pop. Extremely fast, but probably the worst base-stealer ever to swipe more than 100 bases (career 109SB/96CS). Looked a little like Kenneth the Page from 30 Rock.
Runner-Up: Roy Smalley (.258/.350/.419, 4.5). Almost all of his games at shortstop with the Twins happened in the pre-Dome era; by the time he came back in 1985, he was playing first and third almost exclusively (and he's actually listed on the ballot as a DH). Still easily the next-best option in this era.