By default WordPress multisite network orders ‘My Sites’ dropdown menu by website IDs. You can make this easier by reordering websites on ‘My Sites’ menu alphabetically keeping the main blog as top navigation item at the same time.
Reorder My Sites is a WordPress plugin that automatically makes this change as soon activated on a multisite WordPress installation.
Start by installing ‘Reorder My Sites’ plugin in WordPress
Upon network activation, look at list of websites in your WordPress admin bar, they should appear in alphabetical order excluding the main website.