I remember one year when i was around 15 I got a Yamaha DX9 synth for Xmas and I was absolutely blown away that dad saved for it for me and another year when I was much younger all my friends got an Atari VCS and I got a Radofin games console - yuck
It had non-centring joysticks which really just suck big time.
The best was by far in 1986 when I got a Speccy Plus. I still remember the awe!
I can't remember any as the worst, I always liked my presents. My parents got us one for each every year but they usually had a good idea on what we would love to get.