What's the difference between iShowU Studio and v1/HD/HD Pro?

That depends on your needs.

 

iShowU v1/HD are what we call ‘realtime’ solutions. They are suited to a workflow where you want to “record, and be done”.  In other words, when you finish recording with iShowU v1/HD the movie you get is the final product.

 

iShowU Studio on the other hand lets you edit your composition before you turn it into a final movie for sharing. This is a more flexible workflow. But this realtime vs non-linear editor aspect is just one difference.  Keep in mind that iShowU Studio has a color correct workflow as well, thus it can produce more "correct" results than iShowU v1/HD.

 

If you’re doing really quick captures where you don’t need to edit anything, don’t want to freeze frame, zoom in, or change the recorded footage in any way then iShowU v1/HD are fine choices.  

 

Studio on the other hand lets you edit your recording to your hearts content before creating the final movie. So if you stuffed up the beginning or end (or even the middle!) you can easily cut that out. You can turn off/on mouse/keyboard animations half way through if you don’t want them showing all the time, and likewise you can have the camera showing perhaps only at the beginning and at the end.

 

Here's the types of editing operations that you can perform. And, there's nothing to stop you creating further edits after you're initial production. Think of iShowU Studio as "a word processor for video":

• Trimming: It's really easy to trim the beginning and end off of a recording, which is perfect for removing false starts or tidying up messy endings. 
• Split / Cut / Ripple Delete: It's very easy to split the footage into parts; and delete parts you don't want, or even ripple delete entire sections. Ripple delete makes it easy to cut out bad takes during a recording.
• Pan/Zoom: Move the camera in and around the scene. This lets you focus on parts that important to the user, a great way to draw attention to certain areas.
• Audio Annotations: Add additional audio to your project - after the initial recording. Explain what you really meant. Record multiple times if you have to. It's easy to get the right audio in place.
• Editable Camera / Mouse / Keyboard Animations: Choose exactly when, and how mouse and keyboard animations are shown. The text attributes of keyboard animations are now editable in iShowU Studio, providing customisations not available in iShowU HD.
• Annotations: Add pointers and other shapes to highlight areas that you want the user to focus on.
• Gesture Recording: If you're recording iOS footage (from an iPad/iPhone), then this is a killer win...  record the gestures you make, and use these when producing your video. It makes for expressive and user friendly presentations.
• Color Correct workflow: iShowU Studio honors color tagging of source footage, and produces correctly tagged Rec 709 HD footage when encoding. Generally this can be summed up as "it's more accurate".

This is just some of the more common ones, you can download the manual to get a more complete idea.

So, to sum up: Studio will in general provide you far more editing tools and give you a much more professional result, while HD (in some cases) may be quicker to produce a movie.