Best format for long filenames?

I will be having a lot of standard html-pages with rather long names, and I have been wondering which format is best.

word-word-word-word-word.html
word+word+word+word+word.html
wordwordwordwordword.html
word_word_word_word_word.html

Or perhaps something entirely different? Which approach is preferable?

 

I go for word-word-word-word-word.html every time, keeping the original title/heading as short yet descriptive as possible and omitting "stop words" & special characters

 

Yes it is the most readable version. (Thank you)

 

use hyphens. word-word-word-word.

 

Hyphens! And if you are really intelligent you will work out that if googlebot finds it easier to use hyphens to seperate words after the .com/ the same will also apply in the domain name! >

Google Hyphens

Flies in the face of conventional thinking though - I know!