Which type of domain name is more attractive ?

Hyphenated domain names used to give you SEO advantage, but it's diminishing.  Also people can't really remember those domain names.  It's advisable that you choose domain names that do not use hyphens at this point.

Acquiring one way links and creating content are two of the most important SEO tactics because these two are permanent.  Something like tweaking domain name may become ineffective, so ... you may not want to focus on these tactics too much.

Nope.
Every link is good for Pagerank.
But one-way links can be a bit better.

You can use signature links.  You can also submit to search directories to get one-way links.  So called quality one way links are hard to get, but if you're talking about any one-way link, it's not that difficult to get.

That doesn't make sense.  A couple of sites of mine have nothing but signature links, so they ought to count for something.

Try some of the link trading sites.

I would go for non hyphenated. Thats what I use, although I do own both versions of the domains.