What is the best for Search Engines? 1-www.domain.com/keyword1_keyword2 2-www.domain.com/keyword1keyword2 1-www.domain.com/keyword1-keyword2
I believe the third option is the best. hyphens are always better than underscores. in the second option there is no separate sign between the two keywords and it's make it harder to see the keyword by the search engines.
as my limited experiment,no difference between 1,2. but i prefer to -, for there is "-" in domain, so when people input URLS,they are more familiar with "-" than "_". i think search engines maybe consider it.