My son has a Ruger American in 7mm-08 and my daughter a Howa mini in 6mm ARC. Howa has been a bit more accurate, though that could easily be down to sample variation or what I think is a very good case design in the arc.
Both had terrible factory stocks, though that does not appear to you be a concern given your plans. Both have underwhelming DBMs, but again not likely a relevant issue for you.
I don't mind the two-stage trigger on the Howa, and with a very straightforward clip of a spring coil it is now quite good. I put a spring from Mcarbo in the Ruger and it is now acceptable. If you don't mind it two stage, I would definitely give the nod to the Howa for trigger.
Fit and finish, action smoothness, aesthetics, general feeling of quality, all go to the Howa by a comfortable margin for me.
That Ruger came to us in a good used deal a few years ago when things were financially a bit tighter for us than they are now. The Howa was a decision based on the appeal of the mini action for a very compact kids' rifle, and the appeal of a mild recoiling 6mm. If there was an easy way to do a 6ARC Tikka, I would likely have gone that route and just dealt with the extra action length. I was not interested in a .243 or CM case size for recoil reasons, and there's still part of me that thinks a .223 Tikka would have been the better choice. All that said, I've ended up quite pleased with that Howa.
Do you hand load? The fast twist .243 Tikka suggestion is a solid one, though as you said the factory heavy .243 selection is very slim.
I'd rather have a sub-optimal case in a Tikka than an optimal case in a Ruger. You could easily go Ackley in it, and get good modern angles on your case if that's a big deal for you.