Having owned both a BMW S1000RR and the 1299s, I can tell you my real World experiences.
The BMW S1000RR is hands down, the best all around Motorcycle for sale right now. It's stinking fast right out of the box, it's comfortable, it's a great commute bike ( I put over 54,000 miles on mine, so you're not going to find a lot of people with as much seat time on one as me).. Overall, a fabulous bike. Mine had a full Ti Akra race system, a custom tune and a BMC race filter and made 186 RWHP on a stingy dyno.. An absolute animal above 11,000 rpm. I regeared it, because it was all off for my local tracks.
BUT. it's heavy and feels it. The suspension, while not crap, is certainly not top notch. At the track, I am running about 7 seconds a lap off lap record pace and that's about all the BMW has in it in my hands.. It gets REALLY sketchy once you push it hard (I had the NON DDS suspension on mine). The brakes are really, really good. It steers quite slowly and the turn in is lazy.
The downsides? The engine needs to have its nuts revved off to get the best out of it. Great for straight line racing and freeway roll-ins, if that's your thing, but not so good for track use. It has to be regeared. For instance, at all 4 of my local tracks, it has major issues in various corners being out of the powerband, or being way too high up the rev range in a lower gear. Regearing helps, but then it ends up being a pain in the ass changing sprockets for each track and then back for street use.
The 1299, is an entirely different animal. On paper, they seem closely matched, but they are NOTHNG like each other.
The 1299 is around 30 lbs lighter, but it feels more like 50. The suspension on the 1299 is far superior (as it should be, since we paid $8,00 more for the 1299 than for an S1000RR). The 1299 steers and turns in like a 600 class bike (I also own a Triumph Daytona 675R, which was my previous handling benchmark for Motorcycles), once you get the 1299 set up properly, it's phenomenal; it rides better than the BMW, it handles better and it is far more confidence inspiring. The 1299 also transitions far faster and with less effort.. Flicking the bike from side to side is near telepathic and far less of a wrestling match than on the S1000RR.
With the few simple mods I have made to my 1299, I can tell you that it's faster in every regard than my S1000RR was; the only caveat I have, is that I still haven't pushed my 1299 above 170 mph, but up to that speed, my 1299 as it stands, is quicker than my S1000RR ever was.
The 1299 has better electronics, the BMW had crude traction control, utterly crap wheelie control and the electronics basically fought you if you rode past a certain level. At the track, I turned off all the electronics, including the TC, because the bike kept trying to save me when I didn't need saved.
The brakes on the 1299 are by far the best I have ever experienced on a Motorcycle.
Both are amazing motorcycles, but one is a fabulous all rounder and one is a focused, difficult but challenging beast.
I was going to buy a 2015 S1000RR, but decided what I wanted was a bit more personality, a bit more passion and a bit more focus and the 1299 has delivered WAY above my expectations. I have now ridden my buddies 2015 S1000RR a TON and as good as it is, there is no way in hell, I would take it over the 1299.
Each person has different needs and wants. Some will go for the all rounder, competent BMW, some want a more raw, fun experience and some will go with the Yamaha, which seems to be somewhere in between the BMW and the 1299.
That's my input after owning each of them and putting almost 7,000 miles on the 1299 and 54,000+ on the S1000RR.