43mm vs 77mm for travel

I have 15, 43 and 77 lenses. No experience with the 21. You may need the extra wide angle of the 15. My 77 is not always sharp and suffers from purple fringing. The sharpness depends on the distance to the subject.

My 43 is very sharp and compact. Generally not as much purple fringe although is not really an issue for me with either since I use lr4 and has a very effective pf tool.