Over the years I've been round & round with this and spent a lot of money buying-selling-trading only to realize that the AR15 is perhaps the most logistically sound, most efficient design from which to fire the 5.56 & .223 cartridge. The one non-AR I'm keeping is the AUG A3.
AKs in this caliber typically suffer from reliability and lack of standardization of parts & mags.
HK93s are great, but they're heavy, expensive beasts with a very small & finite pool of parts and support.
The SIG 556 has been riddled with issues from day one, and it seems SIG refuses to give the people what they want. Garbage furniture and a bolted-on optics rail are big negatives for me. The genuine Swiss SIG 550 series rifles will run you $5k+. Swi$$ parts aren't cheap either.
I like the SCAR, but the stock system is weak and there is one single source of parts and the knowledgebase for repairs is slim.
The Mini14 isn't so cheap anymore, which makes a decent AR a much more viable choice for accuracy, reliability, speed, manipulation and long term support.
I really like the Daewoo rifles, but there is hardly any market support for them at all. It's all fun until something needs to get replaced. Then the headaches begin.
The ACR has been a huge letdown for most of the folks who were impressed with the design/build specs of the original Magpul showing. High price, unestablished rifle, single source of parts, etc.
I haven't spent time with a Tavor, but at the moment they suffer the same problems as other choices, parts, support and knowledgebase are slim pickins. There's a lot of reports of them being overgassed.
The FS2000 feels like you're holding a big tuna fish. I'm not a fan of an inaccessible action. FN generally makes great stuff though.
The AUG has been around since the 70s, and Pete Athens has always been selling parts for these rifles here in the States. They take some getting used to, but they are excellent quality guns. Expensive, yes, but they are a sustainable option unlike many of the other choices out there. Mags are cheap right now. There's a good number of options for outfitting one, and more AUG models/options are in the pipeline. The trigger pull and non-free float barrel are the only limiting factors in accuracy. I find them to be extremely well designed and that has been proven in their Military & Gov't service around the world. I think they are just under $2k right now.