Personally, I created an album, in iPhoto, called "Photo's for iPad" and moved all the pictures that I want on the iPad into it.
Then, with the iPad connected to my computer, I select the iPad in the sidebar and click on the Photos Tab.
On that page, you get the choice of Syncing "All photo, albums, and Faces" or "Selected Albums, Events,and Faces"
Click the Selected Albums choice and then, in the pane below, choose the album. In my case, "Photo's for iPad"

Next time I sync the iPad, only those pictures that are in that album will tranferred to the iPad and everything else will be removed.
Now it is only a matter of removing any picture that you do not want on the iPad from the selected album and it will be removed at the next sync