Keep in mind the following is based on my own personal experience flying from Canada to Uganda multiple times per year.
Thinking back to my overseas flights across the Atlantic, I have recently flown with British Airways, United, and KLM.
British Airways were good. The plane felt clean and comfortable, staff seemed professional. The food served in economy class was decent for airline food. Not my favorite airline to date but very, very close to a favorite for that trans-Atlantic journey.
United, well what can I say I got there with no issues. Although I cannot say there was anything wrong with the flight itself, I felt there was nothing spectacular to report back on.
KLM – of the three airlines I have taken this past year to Uganda, KLM is by far my favorite. Their super professional staff and reliable flights make it my first choice from Canada to Uganda and back. The prices I pay are average for this journey, not the lowest but certainly not highest. But the value is worth it considering they can get me there with only 1 layover (Amsterdam) on the way there, and at most 2 layovers (Nairobi & Amsterdam) on the way back. I have also never had a cancellation.