I have worked in both Lagos and Kigali on the 737.
I would imagine you are talking about Arik versus Rwandair.
Arik offers a very good rotation - Rwandair did not offer the same. 4 weeks on followed by 4 weeks off is hard to beat. However LOS is a very hard place to live and work.
Rawandair is a worse rotation but Kigali is a much nicer place to live.
That's it in a nutshell! And a difficult choice to make. Can't help more unless I know more about your personal circumstances. If you are single and unattached then I would go for Kigali. If otherwise then LOS could be your thing as you get more time with the Mrs (although YOU will pay for it).
Very glad I have retired now as I only have to choose which pub with real ale I will spend my cash in tonight.
Kind regards
Exeng