I have both scopes you referenced. I have a Vortex Diamondback Tactical 4-16x40 on my .223 Ruger American and an Athlon Argos BTR Gen 2 6-24x50 on my Bergara B-14 HMR in .308 Winchester.
The Vortex (and Ruger American) were what I got when I got back into shooting (I'd shot previously, but only 22 LR). The Athlon was the next scope that I bought and originally it topped my Remington 700 PRC in 6.5 CM. Both are great scopes, but between the 2 the Athlon is better. Glass quality is about the same, however I like the turrets MUCH better on the Athlon. Also, having a zero stop has become a must for me, which the Vortex doesn't have. The Diamondback is probably pretty similar to the Gen 1 Argos from what I've heard (no zero stop, mushier turrets). The Athlon Argos also has an illuminated reticle, if you care about that (I really don't). Speaking of reticles, I prefer the EBR-2C on my Diamondback over the APLR2 that is in the Argos. That being said, both are more than usable and it really just comes down to preference.
I've taken the Diamondback out to about 600 yards on the 223 (I'm sure I could get more out of it), and have shot at 1000 yards with the Argos (both on the 6.5 CM that it previously topped as well as the 308 it's currently on).