WordPress Media Manager 3.5 – default link to

You can do what you want by overriding appropriate Backbone view, which is responsible for rendering attachments display settings form.

plugin.php

add_action( 'load-post.php', 'wpse8170_media_popup_init' );
add_action( 'load-post-new.php', 'wpse8170_media_popup_init' );
function wpse8170_media_popup_init() {
    wp_enqueue_script( 'wpse8170-media-manager', plugins_url( '/js/media.js', __FILE__ ), array( 'media-editor' ) );
}

media.js

(function() {
    var _AttachmentDisplay = wp.media.view.Settings.AttachmentDisplay;
    wp.media.view.Settings.AttachmentDisplay = _AttachmentDisplay.extend({
        render: function() {
            _AttachmentDisplay.prototype.render.apply(this, arguments);
            this.$el.find('select.link-to').val('none');
            this.model.set('link', 'none');
            this.updateLinkTo();
        }
    });
})();