Choose between open declaration/implementation on Ctrl + click in IntelliJ IDEA

There is not a built-in option for this. You would need to configure a custom quick list to do such.

1. Open the Settings dialog and go to "Quick Lists" (It's under "Appearance & Behavior" in IDEA 14)
2. Click the add button to the right of the middle pane
3. Give your list a name
4. Click the add button to the right of the far right pane (where is reads "no actions")
5. Add the Go to Declaration action (Main Menu > Navigate > Go to Declaration)
6. Add the Go to Implementation(s) action (Main Menu > Navigate > Go to Implementation(s))
7. Click Apply
8. Go to Keymap in the settings
9. Under the "Quick List" node, find the Quick List you just created and map a short-cut (keyboard or mouse) to it. You can, of course, remap one of the shortcuts used by the Go to Declaration or the Go to Implementation(s) action
10. Click OK to close out of the settings and give it a try.

Note that in the quick list that opens, you will have numbers next to each action for quick selection.

Edit: Adding a screenshot of final quick list for additional clarity

I was looking for the same thing, because I was also used to it in Eclipse. Nevertheless, in 99% of the cases, I went to the implementation. If that's your case too, you may consider changing the Ctrl+click shortcut in IntelliJ:

• Open File → Settings... → Keymap
• Search for "implementation", and identify the item "Main menu → Navigate → Implementation(s)" in the list
• Right-click the item and choose "Add Mouse Shortcut"
• Add the Ctrl+click shortcut by making a Ctrl+left click on the window
• When hitting the OK button, you have two choises :
  • Remove the existing shortcut (opening the declaration)
  • Leave the existing shortcut : In that case, when using then Ctrl+click, both the declaration and the implementation will be opened (at least when they are in different files)

I know this answer comes like 2 years too late, but hopefully it may help others?

EDIT : This shortcut also applies when you want to navigate to the declaration of a super class. Therefore, my "99%" first declared above drops a bit. I've added the ctrl + right-click as a shortcut to go the declaration (which conflicts with no other shortcut - but you need a mouse with at least two buttons...).