Relative Font Size

When using relative font sizes in style sheets, I'm wondering if it's more preferable to use the "em" unit rather and percentages.  W3C seems to recommend the "em" unit, but I'm curious if percentages are ok?
 
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for example:
 
.body   {FONT-SIZE: 70%;FONT-FAMILY:verdana,arial;color:#000000;}
 
vs.
 
.body   {FONT-SIZE: .75em;FONT-FAMILY:verdana,arial;color:#000000;}
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Thanks!
Eileen
 
 
Eileen O'Brien
Hubbard|One
p: 312.939.5000 x 223
e:  <mailto:eobrien@hubbardone.com> eobrien@hubbardone.com