My choices, any will do but they are in my preferable order
-canon 24/28 2.8 is
Any of these with a 50mm 1.8 would be great.
-zooms for travel/walk around depending on your shooting style, f4 with the 6d's iso is ok
-primes for fun... The BEST lenses to improve your photography.
But I think the sigma 35mm 14 would suit your needs. It is hard to invest in such an expensive lens such as the 35mm 1.4 ii and then have your ok 100 f2 and 200 2.8, because you always say... "oh I need to use my better lens. "
The sigma 35mm 1.4, along with the canon 40mm would be a good 1000 dollar buy, but any combo of the primes would be good.
But even just get one of the zooms I mentioned, and test what range is your favorite. Although primes make you think abou the image and make you better, sometimes you could actually do better with a different focal length. Be mindful of how wide you want to go for a prime. And also, canon made the 24mm is, 28mm is, and 35mm is specifically for the 6d really, there for the one handed enthusiast, who likes to shoot from the hip.