Pretty sure it was the SNES Shadowrun for me. I was already familiar with Shadowrun from books and the tabletop RPG and I got a Swedish copy of it because the english version wasn't available yet. I eventually got a used copy of the English version as well.
I did play Deus Ex at some point after and I had great time with it, but I don't think I ever played the second game for some reason.
I recall trying the OG Syndicate game at some point as well, but I'm pretty sure that well after I had exhausted the first 2 X-com games, and I was looking for more strategy stuff. No idea really when that was, but definetely after Shadowrun.