Anything but Ubuntu! That includes [A-Z]buntu and all other variants, and Debian. There used to be lots of great, easy-to-use Linux distributions before Canonical got its hooks into Linux and began corrupting it with bad habits like sudo. Debian is little more than a monument to the character flaws of RMS, the worst possible distro to build on.
If your goal is to learn Linux, then you need to start with a system that lets you see the Linux. Installing a soft and gooey distro may look "just like Windows" but at the cost of exposing you to any Linux at all. I started with Slackware in 1995, and if I had to do it over, I'd start with Slackware again. Just uncheck the "x" and "xap" package groups, so you don't get distracted by the X Window System and many big, bloated window managers and desktop environments--they are not Linux. If you spend all day pointing and clicking in a WIMP, you'll never find Linux. Install Slackware without X. Read the boot messages. Discover your computer's hardware through the messages and commands like `lsmod'. Read the Slackbook. Try to build a Linux kernel specifically for your computer. Try again until you've mastered it. That's Linux.
Grub is not Linux, and it's a bit porky to use as a bootloader to learn Linux with, however it's likely to be the only bootloader you get to use these days. LILO was nice and simple...it's a shame that Linux has been defaced by so much cruft. You'll need to learn Grub to be able to learn Linux, sadly. The BASH shell and GNU utilities are not actually Linux either, but come with most every Linux distro, so you'll want to learn them. Just take care to bite off only as much as you can chew and swallow in one setting. There's a lot to digest, a lifetime's worth of learning from soup to nuts.