Benefits of four separate domains:
If you own domains with your keywords in them, then the keyword relevancy would be a reason to go in that direction.
For example:
Assuming those aren't the domains in question, and they're more like revolutionincwebdesign.com, then the keyword relevancy won't be much of a benefit.
Pitfalls of four separate domains:
As Gareth and Brina said, you'll be splitting your domain authority and you'll need to quadruple your link building efforts just to stay even.
Bottom line, unless these are killer domains, or you're a holding company with different and unrelated business, it's most likely better to focus on building up a single domain.
You can always use the keywords in the filename: