Mine was a text based one I got from Spectrum magazine Crash. I think it was called Artic?
After that I got heavily into the text based scene and became a regular customer of Zenobi who published the classic Behind Closed Doors Trilogies as well as some other more serious based adventures.
I've entered a bit of nostalgia now so please excuse me as I continue...
After Zenobi I have fond memories of playing Level 9's adventures Scapegoat and Ingrid's Back and Camelot. For me they were the pinnacle of adventuring on the Spectrum.
I feel a sudden urge to dig out the speccy emulator now!