I have always bought or received in trade inexpensive plinking or target ammo (9mm 115gr FMJ)... I always mixed it together in a ammo can. that was until recently when I was really noticing a accuracy and power difference . I mostly buy and shoot both Winchester white box, and Federal Champion. so I set out to seperate and keep track of what ammo works best even for just plinking...  I know there are alot of haters out there but the Winchester white box 115gr FMJ works best for me.  I have never had a FTF and after a few thousand rounds they all seem pretty consistant power wise.  Federal Champion 115gr FMJ I noticed a difference between rounds out of the same box, some were very low powered and quieter, some had a substantial muzzle flash, and some would fly many inches off target and tear the paper like the jacket was coming off.  Comparing the two, Winchester WB  was more accurate, had a very consistant louder more powerful feel....
I have shot  quite a few other brands and grains but never enough to focus on.  I also try to shoot my self defense loads at least once a month  I currently use  Hornady critical defense 115gr FTX..they shoot very similiar patterns to the Win. WB I practice with.
any thoughts?  

my observations mentioned above were while shooting my Sig P320, Sig P229, Berretta M9, Glock 43, and my CZ P07.

I like the WWB the most for cheap plinking, I've never had a problem with it.  I believe people that said that  they have had trouble with it, but that hasn't been my experience.  If I run into a shitty lot, my opinion may change, but that hasn't happened yet.

I've had WWB issues but I chalked that up to the cranked up production during the great scare of 2013.

My P320 does not like anything less than 124, my Shield hates anything less than 147, my P07 and VP9 likes anything and they both group the same no matter the ammo.

I took a class back in October.  The only ammo-related malfunctions in the two day class occurred with WWB, in both 9mm and 40.

I had issues with wwb 115gr in my P320 compact. It would fail to extract every magazine or two. I got a different extractor spring pin from Sig and ever since it's been 100% reliable. Seems to be loaded fairly hot. No perceived difference between it and Winchester 124gr NATO for me.

WWB performs very well for me.  I buy in 100 or 200 packs and have probably shot 1k to 1.5k rounds out of an early P320, Beretta Brigadier, Gock 17&19.  No issues.
For >$10 a box I have no qualms about it.  To get the price I usually have to buy one box at a time but it's part of the grocery trip.

I've never had an issue from WWB or Fed champion. The fed is weak but it goes bang and is good enough for the range.