I have no experience with the Sightron, but I have had the Vortex Viper 6.5-20x44 for 3 years now. And I want to point out, the Vortex Vipers/HST/PST and so on are not made in China, they are made in the Philippines, and also the HST 4-16x44 IS made by Vortex, I think 300whisper may have meant to say Viper instead of Vortex. Just want to clear up any confusion.
The 6.5-20x44 has served me very well, I have used it on my semi custom .260 AI, it is very repeatable and tracks well. I dial for all my shooting, both elevation and windage. I have a 20 MOA rail installed, and I have 48 MOA of usable adjustment, and in my rifle that gets me to about 1600 yds, give or take a touch. I have put about 1200 rounds through this rifle with this scope, and about 500 rounds with it mounted on a .308, and taken several animals, including a deer at 925 yards, a pronghorn at 876 yards, and two doe pronghorn at 465 yards and 440 yards, all shots were dialed and all were 1st shot impacts/kills and only one took a second hit, the pronghorn at 876, and that was only an insurance shot. Pretty much all my other shooting has been dialed shooting at steel or P-Dogs anywhere from 300-1600 yards.
I like the capped tall turrets for hunting, it insures I won't bump them, and if I have time to take a long shot I will usually have time to unscrew a couple caps. My only complaints I would have with this scope is the short eye relief, but being as it is on a braked .260 AI, that is not an issue. My friend has the same scope on a sporter weight Browning A-bolt chambered in 7mm rem mag pushing 168 grain pills at 3075, and if he isn't careful it wacks him pretty good. But, being as your putting it on a .223, I would not be concerned. My other complaint is no zero stop, but if you pay attention you can make it work without it. If you can find this scope on sale, it is an especially good deal, I have seen it as low as $349 on sale at Cabelas or Sportsmans.
I also have used two different Vortex Viper HST 6-24x50's, a Viper PST 4-16x50, and an HS-LR 4-16x50, and they are all good scopes too, if you are able to save a touch more. If not, the Viper 6.5-20 will also serve you well with a couple less options (zero stop, exposed turrets, more reticle options, ect.) And it goes without saying, but is also notable, that Vortex has one of the best warranties of any company in the sporting market. And they offer a killer L.E./MILITARY discount program, if you are either.
