You should be able to use almost any EQ on anything and get a reasonable result. If harshness is being added, maybe it is you that is adding the harshness with what frequencies you may be boosting or cutting.
Unless of course you set identical settings on say two EQ plug -ins and one sounds better than the other for some reason. Then you have a case maybe.
One EQ that I have recently bought is the Pultec EQ from Nomad Factory and it sounds amazing. Especially in a mastering situation. I also use and like the LP64 from Cakewalk as well. It is very transparent and capable of some very precise work and it does not alter the sound of your mix.
(integrity I mean EQ obviously)
Here is the Nomad Link for those who are keen:
http://www.nomadfactory.com/products/pulsetec/index.html I was lucky to get it as a no brainer for around $30. It has a magic sound and even with no EQ being applied it has that elusive feel you get after passing anything through it. It takes a little getting used to as well as it does not operate like a normal EQ either. Be aware of what it does with everything set flat on it too! It is fantastic that you can switch any of the three individual areas or bands off and it works great in conjunction with another EQ like the LP64.
Also anything PSP that
Linear Phase mentions would be good too. I can vouch for their limiter that is for sure.
Price is some ways is going to be a bit of a clue as to an EQ sounding good or better than average. If it costs over $100 then there is a good chance it will be pretty good at what it does.
I find the areas that need the better sounding EQ's is mastering much more so that the sort of EQ's available for use within a multi track session. Most of the EQ's bundled with nearly every DAW sound pretty good to me being used in that mode. It is still much more about making solid and good EQ choices.