I'm an avionics aircraft mechanic. The first-ever aircraft I worked was a Boeing 737-800. It was a great experience for me even stepping on it for the first time. I worked later on Boeing 777s, and 787s now, but the 737 will always be my fave aircraft -- it helped me understand so many systems. Also, it's maintenance-friendly. Component-replacement and snag-rectification-friendly.
I did my first engine change, too, on a 737. It was an awesome feeling to be involved in working on it. The 777 gave me a new and advanced look at avionics, which other manufacturers were still so behind on when it came into being. With the 787s, it's totally a new game now. I'm trying to learn more on it -- still a long way to go.
Thanks to Boeing for what I am today. Also, congrats on your 100th celebrations.