Sigma 30mm f2.8 or Sony 50mm F1.8

I don't think IQ is meaningful here. 30mm on nex with about 45mm equivalent FF field of view compared with 75mm (50mm@apsc) is just much more useful for landscape, street and environmental portraits.

I have a minolta 24/2.8 and konica 35/2 and I virtually never touch my 4x beautiful 50/1.4 lenses except for portraits and tight/distant landscapes where their creamy bokeh and sharpness shine.

Even my tokina 12-24 gets more airtime on my nex.