Write cutting edge 2.x code - and prepare for 3.x.
Note that most of the functionality will be moved to a separate Shim plugin.
See Tips-Upgrading-to-CakePHP-2.x and the plugin in general.
Don't use named params anywhere, they will be gone in 3.x anyway.
Default settings for Paginator, ... can be set using Configure:
$config['Paginator'] = array(
'paramType' => 'querystring'
);
Just make sure, that your AppController extends the Tools.MyController class.
Tip: Using the Shim plugin this is already done for you out of the box.
You can also set Configure::write('Shim.warnAboutNamedParams', true) to get a warning if
any of your code still uses the deprecated named params.
In 3.x there will be a FlashComponent instead. Mine also provides stackable (multi) messages. See https://github.com/dereuromark/cakephp-tools/wiki/Flash-messages for details.
Backported StringTemplate class (from CakePHP3.0) can be used to use template based rendering of HTML tags.
FormExt and HtmlExt helpers also provide extended functionality and 3.x shims.
Also see the Shim plugin for details and documentation on more possible shims you can leverage.