Any of the latest generation ARs, ACR, SCAR, ARX-160...
Ach, rails, pfff

l would definitely love to try out a new ARX-160 though
Epoxy: My trigger breaks like glass, must have lucked out.
But all satire aside, as rifles go the newer ones Blaxsun mentions above only just showed up last week so to speak.
I'm not aware of anyone fielding the ACR and beating up on it daily. Are there any reports of how it and the others perform after 10,000 rounds? 30,000 rounds? SIG has test rifles that have fired 100,000 rounds and are still working.
Just because its new does not mean its the best.
The HK, FAL and even the AR have stood the test of time and been put through hell, we
know they will hold up. I've personally seen a G3 get abused so hard it was unreal, it kept on firing without a hitch. From what I've seen I believe the 55X to be equally tough.
Yes its heavy but it keeps running and most here seem to forget about the 551 when comparing it to other rifles with shorter barrels. Much more handy than the 20" model.
As for the right sided charging handle, while playing cowboys and indians in bandit country you would be walking around with one up the tube anyways and when you change mags you use the bolt catch.
If you had to clear a stoppage (rare with this rifle) cant weapon, reach overtop, rack charging handle with left hand, right hand stays on the pistol grip, game on. Anything more involved, nobody is doing that standing in a field, it is done down on the deck, fix it, carry on. I still use the C7 at work and have shot AR's for years. With a bit of practice running this rifle is no problem at all.
The bolt catch is actually quite nice since as soon as the mag snaps in your thumb just hits it.
Rails were not around when I learned to shoot so I have no use for them. Same goes for bipods, lights, toaster ovens and anything else that gets bolted to a field rifle these days. We did not need that stuff to make hits, all we needed was a sling and later on an optic at best.
I will admit the full size Swiss gets heavy and would become a problem for a small 165-170ish lbs fellow to hump around all day.
My hijack is now over so OP, shoot both those rifles and buy the one that calls to you.
I buy what I like and don't care how much things cost, I just save up for them. I bought my SA here used for $2600..