While, many things may appear to be similar, or even the same, with these powerhouse distributions, there are some sizable differences between them.
TRANSFERRED FROM DISQUS COMMENTS:
Ean Schuessler:
Another important difference between Debian and Ubuntu is that Debian tends to look to the community for overarching technological strategies whereas Ubuntu has a history of trying to impose strategies, with somewhat mixed results. Upstart, MIR, Unity (desktop manager), Bazaar, Juju and Snappy are all examples of areas where Canonical attempted to lead the community instead of allowing a leader to emerge organically. There is a degree of technical risk that comes with this approach.
Antony Shen:
Ubuntu provides user a polished Linux distro, debian on the other hand, provide user a Linux distro based on free software; Ubuntu cares about user friendly, debian care about freedom.
If you have time, debian can offer you more learning space than Ubuntu; Ubuntu is better suited for lazy people like me. 
But I really hate Ubuntu switching main DE to Gnome and killing i386 supports. Maybe someday I have to allocate my time for Debian i386 installation.
I am planning to use any of these . which one will be better in starting .
debian⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
The main difference is the Debian project and Canonical is Debian is 50x the size, and does 99% of the develppment work needed by Ubuntu. Ubuntu has many users, but very few programmers and developers working on the project. The current Debian Stable has 57,000 available packages, and if you want proprietary firmware, you can install it from a Debian repository.
Debian makes it easy to connect an external drive to the PC, and build the entire mirror, so you don’t need to be online to install packages. I keep a local mirror of Debian amd64 and i386 arch’s. It’s about 500x as fast as downloading when you have a local mirror.
Ubuntu requires no skill to set up, so knowing Ubuntu is of zero value in the workforce. Ubuntu is a copy of Debian with some Canonical window dressing and dessert topping thrown in to satisfy users who have ADHD.
Ubuntu is proprietary, for profit software, a model that would have made the development of Linux impossible in the first place. Proprietary models are very poor at development of aoftware and operating systems for PCs.
If you’re talking big iron, IBM, COMPAQ, Hitachi, then proprietary OSs make sense. But then you’re talking $400,000 for the OS.
Even Cray supercomputers use non-proprietary software. MCI purchased a Cray some years back. It reduced two-week computer processes down to 2 hours!
Canonical is in a market that doesn’t need it. Most of it’s customers pay no money, ever. It’s unsustainable when you have Red Hat, which is 100x better, and Novell, taking up the proprietary Linux marketplace since the beginning!
If you want to use proprietary Linux, use something good, like Red Hat. It’s free for private individual use, and Red Hat pours money into its Linux OS like there’s no tomorrow. Oracle Linux is based on Red Hat.
But if you want FOSS, use real Linux, not something made for ADHD sufferers, women and children! Have some self-respect people! No offense to the women out there, but working for you is optional. You can always get married and have babies.
In fact, that’s what I like women for. I’ve never met one who is very skilled in data-processing. But maybe that’s just because I don’t associate with feminists.
Ok, got off the track a bit! But just talking about computers for the entire thread gets pretty boring. I apologize if I offended anyone! I hope you can forgive me!
Debian and Ubuntu are both Linux-based operating systems, but they have some differences.
Origin: Debian is an older and more established Linux distribution, first released in 1993. Ubuntu, on the other hand, was first released in 2004 and is based on Debian.
Package management: Debian uses the Advanced Packaging Tool (APT), while Ubuntu uses a customized version of APT called Ubuntu Software.
Release cycle: Debian has a slower release cycle and tends to focus on stability, while Ubuntu has a shorter release cycle and focuses on incorporating the latest technologies.
User interface: Debian provides a more traditional desktop experience, while Ubuntu features a more modern and user-friendly interface.
Community: Debian has a large and diverse community, while Ubuntu has a smaller, more focused community with a strong focus on user experience and ease of use.
Support: Debian provides support for a longer period of time, while Ubuntu provides support for a shorter period of time, but offers more frequent updates and upgrades.
Overall, both Debian and Ubuntu are reliable and popular Linux distributions. The choice between them will depend on the user’s specific needs and preferences.