Mid-pairs

Another simple NL ring question: What to do with midpairs preflop? Let's say deep stacks, position, and 0 to 1 limpers. Raise and play them fast or limp and play for set?

With more limpers/bad position, should I be more likely to just play for the set? I'm just trying to learn some general principles here.

I play multitable slightly passive 50NL.

with mid-pairs (66-99?) I generally limp in EP and raise in MP/LP if it's folded to me, and call small raises when the stacks are deep enough. Sometimes I'll put a lot of pressure on small stacks with 77-99. 99 I always raise with regardless of pos.

Open-limping is not that great, but I'll do it sometimes as the tables are relatively tame.

When people reraise my raises and I have a mid pp, I look at the size of their raise, the size of their stack (and mine, obviously, but I'm usually around the max buy-in), and how aggressive I'm being perceived before I call. So many people min-reraise that I get really good odds to hit a set.