Use spaces by default

Doesn't sound like a good idea. Not only elementary coding will happen in elementary OS. I'd prefer tab to be tab by default.

In IRC just now, 15 minutes into debugging Python script:
voluntatefaber> shnatsel: my fault! I used 4 spaces instead of tabs

It is better to use tabs by default because they are necessary in some languages (like in Python) and work however with all of them

Actually, in Python the advice is to use spaces instead of tabs. See http://www.python.org/dev/peps/pep-0008/, where the designer of Python tells us to "Use 4 spaces per indentation level." For Haskell, it is also prefered to use spaces (http://urchin.earth.li/~ian/style/haskell.html). In short "tabs are evil" (http://www.emacswiki.org/emacs/TabsAreEvil).

Unless the user is coding in Whitespace (http://en.wikipedia.org/wiki/Whitespace_%28programming_language%29), changing tabs to spaces is highly preferable.

Also, it seems appropriate to remove trailing whitespace by default.

When I learnt Python my tutorial said that the tabs are necessary in Python but however I already think that have tabs activate by default isn't bad. The 'tab' key button is supposed to insert tab, not spaces that have the 'space' key button.

I think this sounds like you're trying to optimize for an edge case.

I believe the majority usage of Scratch on elementary OS would be just fine with spaces and it would go well with the majority coding guidelines.

This is just one more of "the little things" that stops developers before they can start coding. It's really lame to have to add "flip the switch to spaces" in the developer guide when it's our own app on our own OS.

If for whatever reason a developer needed to have tabs instead of spaces (which I do believe is the minority case), there's no reason they can't go to preferences and flip that switch.

Another option would be to have tabs and spaces switch intelligently. So for any language where spaces actually did cause some compiling problems, we could enforce tabs.

If the problem is only about programming, we could have the "spaces instead of tabs" added by the euclide plugins.

We should think what's the best default for the average Joe, not a programmer. Scratch is a text editor, not IDE, we have euclide for that.

Dan I said this only for a reason of consistency ("The 'tab' key button is supposed to insert tab, not spaces that have the 'space' key button") but however, following also Andrea, scratch can use spaces by default

This will be fine for files started from scratch, but for files which originated elsewhere 4 spaces instead of tabs might be a really bad idea.
I'd expect tab key is expected to insert a tab. If my coding style requires spaces instead of tabs, I'll check the text editor settings for sure. However, if my hypothetical coding style requires tabs, I'd expect tab key to insert tabs and wouldn't check what's really set in the settings. So please, don't screw people hacking something aside from elementary.
IMHO the best way to solve this is to add coding style presets to Granite.