when building links for home page which is best www.domain.com or www.domain.com/index.html What is your thoughts>>
Usually www.domain.com is the standard version to build links for. Pick one version and stick with it when getting backlinks.
the more simple and short domain names is preferrable and liked by search engine while indexing and also easy for the users to remember
I would not suggest you to go for index.html homepage. Keep it more simple and real, instead of making it complicated I have experienced this in the past and has been running around with all different type of links directing to my homepage as well as index.html.... confusing
I have never used index.html before, but it makes sense to keep things consistent and if you are trying to rank for domain.com then build links for domain.com.
That's why if your website still direct your users and browser to your example.com/index.htm page, use redirect so that all your homepage link building would be more consistent and acceptable for some directory submission sites and other submission sites.