I was very frustrated trying to change the default blog layout without creating a menu item for each blog section of my site. I even created an override, but it wasn't the layout that was the problem, it was the parameters that were being passed.

So, there had to be a place where the default parameters are set, but it took me a while to find the little buggers. I had looked in the db for settings, in the file system for .xml or .ini files and finally I found that they are set in components/com_content/views/view.html.php at about line 50.  The second parameter is what is used if nothing is passed -- the default setting:
// Parameters
$params->def('num_leading_articles', 16);
$params->def('num_intro_articles', 0);
$params->def('num_columns', 1);
$params->def('num_links', 0);
$params->def('show_headings', 1);
$params->def('show_pagination', 2);
$params->def('show_pagination_results', 1);
$params->def('show_pagination_limit', 1);
$params->def('filter', 1);
... [etc] 
Simply by changing those numbers I was able to change the default look of my Blog View layout.