Which is the best, simple to use Github desktop client to use with 18.04 ?
Didn’t know there are desktop clients for Github until I saw your question. I checked out the one from Github and it seems to be for advanced tasks to make extended commits and collaboration in general even easier.
I have used SmartGit, SourceTree and GitKraken and I can say that all three are very decent clients now. My personal recommendation is for SmartGit - although it is commercial, it is just better thought out that the others. GitKraken comes in free and pro versions - but the free version is very good. SourceTree has been hampered by a poor choice of palette (insufficient contrast) and a rather fussy sign on process. But it is free and I believe now has a dark mode that is less objectionable.
I use GitKraken because it is available on most platforms and supports Github, Gitlab, and Bitbucket