How can I theme some blocks with the same theme? I'm seeking the best practises for theming some blocks using a same template file, but my problem is that blocks may not be used in a same region, and they can also be used in one module that has a bundle of different blocks with different themes.

How can I achieve this?
Block Theme module will be really helpful. You have a select box where you can choose different tpl.php files for each block you configure