AI OnAI Off
Search: http://world.episerver.com/documentation/Items/Developers-Guide/EPiServer-CMS/9/Search/Search/
Find: http://world.episerver.com/documentation/Other-products/EPiServer-Find/
As you can see they're not really comparable. Find wins in all cases as long as you don't compare price.
If you need advanced faceting, highlighting, boosting, spell suggestion etc then it's time to think about Find. Episerver standard is suitable if you don't need a powerful search / lack funds.