I would suggest a businessperson look as recommended by many internet marketeers.

Also consider that websites with photos of uniformed people convert higher numbers of visitors into paying customers.

However, using an image of a cartoon character or realistic fun character is a good marketing strategy (think of Macdonalds).

This website advises Google regarding website conversion strategy resulting in the Google optimizer:

http://www.conversion-rate-experts.com/

…look at the fact that they are using a cartoon image to promote themselves.

Any blogs, tweets can be added to by other employees under a generic image.

If it is just yourself that is actively involved then a shirt & tie/uniform photo would be the best image to project for a personal approach depending on the type of business.
References :
http://affiliate.kickapps.com/service/displayHomePageExperience.kickAction?page=Homepage&as=89515