From what I have seen and studied, all things equal, the order for 100% keyword domains is like this:
By TLD:
1. Local TLD (e.g. .de, .fr, etc.) if the search originates from that locale.
2. .com (seems to outperform .us for searches from USA)
3. .net & .org
Note: I was never interested in other general TLDs as .info or .biz
By Words:
1. without dashes (e.g. Keyword1Keyword2.com)
2. with dashes (e.g. Keyword1-Keyword2.com)
3. without dashes, changed order (e.g. Keyword2Keyword1.com)
4. with dashes, changed order (e.g. Keyword2-Keyword1.com)
The .com domain without dashes, and with the keywords in the right order (Keyword1Keyword2.com) has a significant advantage over the others (other TLD or with dashes). It seems that Google sees it as the official site or something like that.
If there is even just a single character (except dashes) that is not part of the search phrase, you get absolutely NO advantage. To get an advantage the domain must be 100% match with the search phrase. That means TheKeyword1Keyword2.com offers no advantage over SomeLongTextKeyword1Keyword2.com.
From my personal experience it seems that you do not get the advantage immediately when you lunch the site, but after a while (a few months).
It helps if you have:
1. Title of homepage EXACTLY the search phrase / keywords in domain name (e.g. Keyword1Keyword2.com -> title should be EXACTLY "Keyword1 Keyword2")
2. Most incoming links EXACTLY the search phrase, some links the search phrase + other words.
3. Text of H1 tag on homepage EXACTLY the search phrase (identical to page title).
4. Search phrase present in the text of the homepage
Personal results (Google):
1. K1K2K3.net -> ranking #5 with about 20 inbound links, after half a year. The keyword is low competition, low search volume, but I would have not ranked there if the domain would have not been 100% search phrase.
2. K1-K2-K3.net -> just launched, 1 inbound link, #350 in SERPs. I expect a significant jump after I build some backlinks.
Bottom line: 100% keyword domains help with rankings, however, for great results you should couple them with solid on-site SEO and link building.