Gee, we've really covered a lot of ground here - from rifles to ammo to optics to calibers to mags. Clear that reasonable minds can differ on these issues. Not that anyone asked, but I do have a couple of quick comments.
300 BO - I honestly haven't bought any ammo for a while and in this market will wait and hope prices come back down. The last time I bought 300 BO it was about .60 per round for decent stuff, which was about twice the cost of 5.56. However, I do own 2 300 BO uppers and for 7-12" barrels I really think this is the way to go. Ballistics are just better. And I kind of like the recoil of 300 BO, seems slightly less sharp than 5.56 - but maybe that's because one of my uppers is a KAC. Also nice that you don't need a different mag or even bolt carrier group for 300 BO. Plus, if you shoot suppressed subsonic are supposed to be the cat's meow.
AK's - Just not a fan, although I've never owned a high quality U.S. one. Stock is great if you're 4'11", but doesn't fit me at all. I shoot much better with some kind of optic and they're tough to mount on an AK. The triggers suck and until I upgraded mine I had trigger slap as well. Yes, ammo is cheap but you get what you pay for, which in the case of most of the surplus ammo that's available is 2-3MOA. Plus, while the loose tolerances may mean that you can drag it through the mud and it will still shoot, it just feels like the cheap rifle it is.
Mags - I know I'm going to be in the minority here, and I agree that no one ever said, "Gee, I wish I have fewer 30 round mags." Still, I just don't see the need to stockpile hundreds of mags. I have one rifle case that I usually use to transport my AR's in. Have a couple of mags in the attached pouches and I just use those over and over again. I've never really done a round count, but they certainly have thousands of rounds through them. Never had a problem with any of them. I do have approx. 30+ mags just sitting unloaded in some ammo cans and maybe I'll dip into those when my current mags start failing. But to me a mag has roughly the same life as a barrel (a gross generalization, I know). However, even if a barrel has three times the useful life of a mag, you don't hear of people stockpiling 2-3 barrels per rifle. Finally, seems like people have been stockpiling mags for years. By now there must be millions and millions of mags out there. Surely I'll be able to find some widow looking to unload her newly deceased husband's stockpile of 30 round mags for a "fair" price.
Tavor - OP has asked about this rifle in a number of posts. Was just out shooting my Tavor this afternoon. 100% reliability. 16" barrel in a package that's shorter than a 12" AR. Heavy, but really well balanced. What's not to like? (Well maybe the crappy stock trigger). To me the ergonomics are pretty intuitive and with a little practice mag changes are almost as fast as with an AR. Plus, offhand I'm able to shoot this rifle at least as well as any rifle I own. The light weight front and heavier back just seem to work for me.