I'm wondering how guys weigh these two stats.  Does one + play make up for one error? Is one minus play hurt as much as an error?  

If you had a SS  who in 1000 innings made 30 errors, but had 10 plus plays and 0 minus plays, how would you compare him to a guy who made 10 errors but had 0 plus plays and 10 minus plays.  If the bats are equal, who do you play at SS?

BTW, the ratings for these two guys have about equal arms, but their range/glove are pretty much reversed 78/88 and 90/75.

i personally would prefer a guy who gets to the ball.  however neither of those guys is a SS, IMHO... first guy is a great 3B, second guy could get by as a 2B or CF

Not exactly sure who you are talking about on your team because I don't see anybody 78/88 or 90/75 but I'm going to make some guesses.

DJ Bennett: 81/91/80/83
Pedro Tavarez: 92/77/93/84

They've been both about average as ML shortstops, although Tavarez is in kind of a small (only 700ish innings) sample size. Tavarez "sum" of all his fielding ratings are a little higher, but I would lean toward them being equal or Bennett slightly better as a SS. But overall, close enough. I think if I was dead set on having both in my lineup I would play Bennett as SS and Tavarez at CF.

Looking at your team though, I think I would platoon them at SS and play Jackson at CF and Moore at 3B.

To address your question more broadly, you can generally weigh, plus/minus plays and errors equally. I've found a minus play/ error to be worth about .65 runs allowed and a plus play approx .65 runs prevented. Obviously there will be situational variations, and i've seen some argue the weighting is a bit different for infielders vs outfielders, but that's close enough to be useful.

Without doing a lot of research it seems guys with lots of + plays have more errors. I figure that is because they get to balls others can't giving them more of a chance for errors, so I always value + plays the  most.

Plus/minus correlates better with range. Errors correlate more closely with glove.

Yeah, I was more interested in the broad answer, so I was hesitant to make it a "where should I play this guy" question.  

These are very helpful answers though, and it will help me in making future acquisitions.

i have a firstbaseman in steinnrenner who was a converted 2b he currentky has 18 plus plays with no errors, but i dont thonk there is a corralation to chances. because of his range he gets to more balls than average.

Do we even know if HBD and Sim League Baseball use the same engine?

I don't think they're the same. Might have started that way and there logically would be many commonalities. But there are differences. Sim does not factor in arm defensively in any way and treats all 3 OF positions the same. Sim also heavily penalizes fielding for players with no experience at a position and only uses a standard platoon-split factor.

I like high range (plus plays) and have no problem living with errors (low glove rating) especially if he has a good bat. 92 range and 78 glove would be a valuable CF in my opinion.