I've played through Crystal a couple times so I know I got a variety, but I remember in my more recent playthroughs getting a Smoochum on one occasion and a Cleffa on another. I never got a Pichu but always wanted one 8(
I've only played it once, on a no-catch challenge, so I saved before I got the egg. The first time I got Cleffa, which I didn't want, so I reset and the second time I got an Elekid which I kept on my team and it was my second best Pokemon.
The only time I played through Crystal, the egg hatched into a Tyrouge. I evolved him into a Hitmonchan (my favorite of the Hitmons), and he became a strong member of my team. Now I'm tempted to play through a few more times and see what I get from that egg.
Now nobody, nobody, nobody, nobody speaks my name
I'm just another blister in the mouth of shame
A bug in Ender's Game