Magne that is why I stated that certain mics suit certain voices cause everyone has a different voice. That said it is sometimes better to use a mic that as faithfully as possible reproduces what it picks up and then EQ that signal to boost the weak frequencies or cut down on the stronger harsher tones....This is best done using a multiband graphic EQ and of course ears. It is worth considering cutting offending frequencies at the top end rather than boosting lower end frequencies to try to compensate......boosting low end can make the sound muddy and dry sounding and sometimes a "false" sounding vocal. Contrary to common held beliefs it is the middles and top end that create warmth and depth. Thin vocals can usually be sorted by de-essing boosting the middle and cutting back on some of the top....but do not over de-ess. I prefer using roll offs and filters rather than a bassier or more top end mic....although that is harder to do in a live situation.
Here is an interesting article on EQ. It gives a chart of where the human voice fits in with certain frequencies in relation to bass middles and top end.
http://www.behindthemixer.com/content/eq-vocals-101-fix-and-mix
and here is another with more EQ tips.
http://www.behindthemixer.com/content/vocal-eq-settings

PS it is worthwhile reading the replies as they add some other tips and POV.

http://www.soundclick.com/bands/songInfo.cfm?bandID=687727&songID=5238055