Statiscally speaking, the ground of inadmissibility your client is charged with has a lot of weight on the outcome of the waiver.

The standard for many waivers of inadmissibility is extreme hardship to a qualifying relative.  However, statistics from USCIS international operations included here show that although the standard is the same, the approval rates of the different waivers are very different.  Take for example the most common waivers, unlawful presence (INA 212(a)(9)(B)), fraud or misrepresentation (INA 212(a)(6)(C)(i)) and crimes (INA 212(a)(2)).  In fiscal year 2010, 21,688 applicants for immigrant visas were charged with the unlawful presence bar and 18,497 overcame it, an almost 85% approval rate.  In contrast, 6,088 IV applicants were charged with the misrepresentation bar and only 1,450 of them overcame it, a mere 23.8% and even worse than criminal grounds of inadmissibility.  

A table of these statistics is attached here.  If the quality of this attachment is not very good, AILA members can access them though the AILA website here: http://www.aila.org/content/default.aspx?docid=34082 (scroll down to the end of the document), AILA InfoNet Doc. No. 11010669. (Posted 1/7/11).  Again, this is only for international operations.  It does not include domestic filed waivers.

This is a clear lesson in not forgetting to address the discretionary factor.  As shown here, the discretionary factor can have a huge impact on the chances of approval or denial of a particular type of waiver.  Advise your clients properly.