It depends on where either link is coming from. (it also depends on who you ask.)
Some say that one ways are better no matter where you get them from, and exchanges can be penalised. If you are getting the links from related sites, then there should be no problem, as long as that site has not been banned.
To check this, get a visual page rank from any one of the many sites that do this, and then if the site you are linking to has PR 0, go to G and see if they have any pages indexed. (site:
www.site.com) If not, they have been banned for some reason and you do not want to link to a bad neighbourhood. Remove them immediately