I saw the Great Scientist void too!
This is a bit of a situation-dependent thing, although I opted for the Great Engineer as probably the most generically useful Great Person - even if you miss World Wonders they can still be used on National Wonders. I tend not to Lightbulb them, but they've often got tempting technologies on offer.
All Great People have their roles, and it depends upon your objectives at the time (e.g. I'll curse the popping of a Great Scientist when striving for a Cultural victory, whereas vice versa with a Spaceship).