What would you choose? Rifle will be around 6.5lb and want to stay lightweight on the glass also. Looking at the 3-18 range magnifications. Is the vx6 more reliable than the swaros when dialing? It won't get put through the paces constantly dialing up and down on the range but just occasionally on hunts. Looks like the vx6 shares the same spring system as the mark 6 from my reading.

I have both, I love both. both dial spot on. leupold has 30mm tube.

coin flip?

I would go vx6

The VX-6 3-18 weighs in at 574 grams, the Z6 3-18 weighs in at 595 grams. For the $1K more for the Z6, I'd go with the VX-6 myself - lighter weight and I doubt there's a significant difference in glass/coatings/clarity/low-light etc. At least not $1000-1200 difference.
Both should do what you want. One just does it for a significant penny less.

I owned both in the 5-25 and 4-24 models and I liked the vx-6 better overall. The dials are a little better and I couldnt tell the difference in the glass. I never had a problem with either one tracking