The old film cameras (the original FF) came with a 50mm lens because it is so versatile. The same way it would be for your 5DMkII. It is your choice if you want the 50 f1.8, inexpensive, or the pricier, and better quality, f1.4.
35L if IQ is paramount, 35/2 if you want lighter, more discreet kit w/o too much IQ tradeoff. I always feel 50 is a bit narrow, but then I've trained my eye with 35mm focal length over the years, so works for me as a generalist prime.
yeah the sigma might be a better choice (sharper wide open with less issues, atlhoguh not as sharp stopped well down though). I have never trusted sigma AF though, but then again I absolutely don't trust the AF on CAnon's 50mm lenses and I think the clutch on my 50mm 1.4 is breaking already (and my first copy had a bad clutch right out of the box).
