They're usually better than the foreign military surplus stuff. Especially if you're buying for an AR-15/M4 rifle. My AR's have generally hated the cheap steel case stuff.

I would fire a couple hundred rounds of whatever you're thinking of stocking up on, in the actual firearm you plan to use it in, before buying in bulk.

Edit: I got into reloading about a decade ago and haven't bought bulk ammunition since (just components). You can dial in your ammo for your specific firearm, and you can save all kinds of money. I can reload 5.56/.223 for less than 20 cents per round (often closer to 15 cents), and I get to control the quality myself.