First Distro was Yggdrasil Linux for me in 1993, I still have the book, and the disks somewhere.
It was a bit of a bear to configure for your hardware, but once done it behaved well.
Shortly thereafter I switched over to Debian, and have not looked back.
I have tried many distro's on my other machines including the ones at work, but I like to be on stable release at home.

Slackware 2.xxx, i yet use it(v 14.2) toghether to debian and ubuntu currently

My first Linux distro was Ubuntu 9.04 on a 32-bit 486 Desktop, lol !

I believe it was called MCC-interim, but my memory fades. I think it was the summer of '92. The kernel was 0.96c, and it used a minix bootloader (dual boot with windows 3.1).

I started with kernel pre. 1.0 on an 80286 and well before X was born.
Downloaded 40+ diskettes to install and I can't remember which dist. it was.
I had 2 Facit-Twist terminals on serial lines that I used about a year before I fully trusted X.

I have tried a lot of distros, but since many years I use Slackware. When I tried Kubuntu last year, I only had a lot of trouble knowing how f* to configure it for my needs, so it was only a short test before I came back to Slackware.

Same with Redhat - I have no fine control on the system as with Slackware.

Debian

1st distro i used back in the l8 nineties was mandrake on a partioned machine with win 98se. i remember installation was a challenge and it took a few months to get a handle on it all b4 i removed bill gates from my machine ...

1st distro i used back in the l8 nineties was mandrake on a partioned machine with win 98se. i remember installation was a challenge and it took a few months to get a handle on it all b4 i removed bill gates from my machine ... i later leaned ubuntu.
now i run machines with mint and deb ian on this laptop on which i type you an answer

Debian Potato, in college 2001-2004.
Small dalliance with Easy Peasy 1.6 on a Netbook in 2012.
Then MX 15.01 in early 2016. Tried many others, always came back to MX. Because it JUST WORKS!

Debian was my first Linux distro -- prior to that I had had experience with vanilla AT&T UNIX, XENIX, AIX and SunOS/Solaris.

My first distro was Red Hat 5.2 in 1998 or 99. It was a revelation after using Windows and I never quite recovered from the experience. It took about a year or two to learn enough about it to be able to ditch Windows completely. One of my favourites of the early Red Hat distros was 6.2 - I really liked it. I continued with Red Hat through several versions before switching to Slackware. Then came Ubuntu and after that Mint which I am still using.... Thinking of returning to Slackware and its attractive simplicity

Mint 17.0. Currently Mint 19.2. Loads of fun along the way.

Famelix: https://archiveos.org/famelix/, and Kurumin: https://archiveos.org/kurumin/ - in 2004. Both were originally based on Knoppix. Good times :-)

My first Linux was Caldera. I tried RedHat but Calera beat it hands down with the installation.

Ubuntu, but I quickly switched to Fedora, and used it for years. At some stage, I found it was getting unreliable with too many unpolished updates, and I experimented with Suse. I am now back to Ubuntu.