I've used Leupold optics for several years. I am sponsored by Leupold, but I won't steer anyone away from a good optic regardless of brand.
For most matches lately, I've been using the VX-6 MultiGunner with a FireDot BDC reticle. It's as good an optic as you'll find and it's the lightest 1-6 optic available. In the past I've used the Mark 6 1-6, which has very good illumination and is darn tough, but it's a bit heavier and they eyebox is a little less forgiving if your head position isn't quite right. The reticles available are a bit more sophisticated (wind holds and drop out to 800-1200 yards depending on which you pick).
For matches that are intense on long-range distances and small targets (600+ yards, targets hidden in woodline, etc.) I use the Mark 8 1.1-8x optic. It's expensive and heavy, but the extra magnification is worth the tradeoff for those matches.
Other Optic Recommendations:
These are optics which I recommend to students looking for a 3-Gun scope that will last them as long as they're interested in the game.
Swarovski:The Swaro Z6i used to be the go-to scope to beat for a 1-6x optic, but a lot of other options have come around that have more to offer. Swaro has very, very good glass, but their scopes are fragile. I've seen two of them break at matches. The Swaro Z8i is a good option if you're looking for a lightweight 1-8x, but you run into similar issues as far as durability.
Kahles: I really like the Kahles K16i series, they're a great balance of clear glass, light weight, and tough. They're a sister company of Swarovski dedicated to tactical products, basically the K16i gives you all the benefits of a Z6i without the drawbacks. They currently do not offer a 1-8, unfortunately.
Vortex: The Razor Gen II 1-6 is a very popular and very good option, the only drawback to it is weight; it weighs about as much or more than any other manufacturer's 1-8x optic. It's extremely robust, offers great glass and illumination, and decent reticle options.
Trijicon: The TR-25 1-6 is another good option. Their ballistic reticles aren't highly regarded, most of the shooters using them choose the simple Triangle Post reticle, which works well out to 400 yards if zeroed at about 300. The old TR-24 was one of the more popular 1-4 scopes before 1-6 became the de facto 3-Gun standard, and is still a good option for a lightweight close-range variable scope if you need just a little extra magnification 100-300 yards.
1-4, 1-6, or 1-8?
1-6x is has become the standard for a general purpose 3-Gun scope, and my recommendation for most people to buy. 1-4x is still useful as a specialty tool for close-range matches with small targets 50-100 yards, but it's harder to use at real long-range distances 200-400 yards. 1-8x is really nice to have at certain matches like Rocky Mountain 3-Gun and Ironman, where 500-650 yard target engagements in the wind and on obscured targets are common. A 1-8x optic is also useful for shooters with vision problems and struggle to distinguish target from background.
My go-to rifle is an 18" Proof Research-barreled rifle with a VX-6 on top. At four major matches per year, I put a Mark 8 on the same rifle for longer-distance stuff. At a few others, the VX-6 goes on a really lightweight 14.5" Proof-barreled rifle for matches with targets at 100 yards or less.
-Brian Nelson, lead multigun instructorTactical Performance Center