What is the best file format for sharing Illustrator images?

As a novice graphic artist I am trying to gain some basic but important information, one of which is: After creating a project and wanting to send it to a client what is the best file to save it as? I ask this because often the artist is using programs like Illustrator and Photoshop that are not installed on the clients computer. Plus I wouldn't want my file to be edited in any way without my knowledge.What is the best file format for sharing Illustrator images?
Send it .PDF, but proofread very carefully when SaveAs... .pdf because Illustrator invariably misplaces the last word of text in the very center of the screen. It can be under a graphic rectangle. So, save as .pdf, change to line View see if there is a word all by its lonesome.





The last word can change. Say, in one version the bottom paragraph was edited. Good chance that has the missing word. But, on proof 2, the headline got edited. Good chance the last word is in the center. C-r-a-z-y, but I've had embarrasing moments with this.





For other graphic programs, Ill. 7 file format allows the drawing to be imported for other workstations.