For debian and ubuntu, which one should I choose as my personal development system?
Thanks.
Depends on your use case and preference
If you're experienced enough or willing to learn then either of them are equally good and you shouldn't have any problem
If you're new to Debian and are not willing to learn tiny things here and there then you should consider one over the other.
Most of the software is available for both from official repositories. But for some software which isn't available yet in the repositories you have to build from source or consider using other sources(either third-party repositories or deb,tar packages) which may be of a problem as some times you wouldn't find support for both of them. Some support Ubuntu only and some support Debian and some support both(although only certain versions).
And with Debian you should setup some things after first install like enabling non-free section for firmwares and nvidia drivers, fonts,bash completion etc.
Some even expect you to use certain version of one of them like Nvidia cudnn which fully supported only on Ubuntu 18.04 although you can get around these with some manual installation work
Debian is most stable though.