Depends when, but in order:
XL100 (!? - was probably a damn sensible thing to want given my riding and maintenance skills at the time, but a weird thing to lust after).
'86 XR200 (starting to get it, but still making sensible choices).
'87 CR125 (finally, something worthy of lust).
Then I got all realistic and sensible again, and started lusting after things that were vaguely realistic with my dismal school-kid budget, like 10 year old YZ125s.
I've now got an 87 CR125 (which they'll bury me with), and a heap of those YZ125s that were ten years old back then... Still reckon a late 1990s YZ would be a good match for my riding ability, and still like to have a late-80s XR200 in the shed...