I'm not a huge .223 fan, but there doesn't seem to be many good semi-auto .308s.
Going with the .223 do you want a DI or piston system of operation?
If the .223 doesn't fit your fancy you could always go with a AR platform based on 6.5 or 6.8
For myself, If I'm going to be throwing a good amount of bullets downrange, I prefer to get a caliber that is relatively cheap to buy by the 1,000 round case.
What is your definition of a "good" semi auto .308? People tend to forget that you have cons with semi autos (hot barrels don't help accuracy most of the times), and IMO those cons tend to increase going with a larger bore gun unless you don't mind spending the money. That's not even taking the mags into consideration. PTR brand and FAL types are another option in that caliber.
Only personal opinion, with a .308, you have some distance to shoot, no problem. However, I've just found that I'd rather load for a .300 Win Mag and take my time shooting longer distances than loading for a .308 and loading up 20 round mags because the ammo goes quicker, at least with me, I've also found, again, only me, that if I take a larger caliber gun out to shoot, if I'm not shooting at least 200 yards minumum, just seems like a waste. Then, if you aren't shooting some quality type ammo, you can be all over the place when you start to push the distance.
If you want a Ruger, cruise the classifieds on the gun boards. Here in NC there was a Ruger 556 that a guy wanted to unload (LNIB) for $1,000 shipped, and it was the newer model, not the "E" (seems in the short time Ruger has had this model out there, they have had multiple models). My understanding is their first model had some issues with cleaning, but Ruger never interested me in a black rifle, so I never really looked into it.
Just remember, a $400 rifle can shoot just as good as a $1,400 one. Comes down to what you want to make work, and practice, practice and more practice never hurts LOL Then again, you can spend money and go in circles. Been there, done that LOL