Domain choosing - which is best?

Ok... this is just way too simple, especially since people talk about this all the time here, but I need some quick advice as I'm in the middle of making this all-important decision that can affect my entire future online.

I have my eye on a couple of domain names for a new PLR site and can't decide which determining factor is best:

keyword target or product target

Keyword target would be a hot keyword related to what I'm offering.

Product target would focus on the product rather than an exact keyword. (I don't mean actual product name, but general product category).

For instance: would it be better to stick to the keyword that most people are searching to find this product or is it better to spell out my exact offer (which will incorporate part of the keyword 'articles')?

I've read so many different opinions on this that I'm not sure which is best. Hyphenation is not good, apparently, but it would make my chosen domain name read properly. Without the hyphen - the 2 words run together read as something else.

Also, how much attention should I pay to the length of the domain name?
My choices range from 13 characters to 18 but the longer is more descriptive.

What's your view on this?

Thanks.

Sylvia