It appears I normally use 'utf8_unicode_ci'. However, I don't know if that is the best collation to use. I searched Magento StackExchange and was suprised I didn't see a question/answer on this topic, so thought I would post this to see if there is a consensus view on this question.
utf8_general_ci will work.
For explanations as to the differences between the two, consult
to find which will give you better results.
Magento\Framework\DB\Ddl\Table you can find some hardcoded database options stored in the
protected $_options = ['type' => 'INNODB', 'charset' => 'utf8', 'collate' => 'utf8_general_ci'];
However, as Fiasco Labs' answer point out you can use
utf8_unicode_ci as well.