I have been using DNA testing since the mid 90's, first with The National Geographic project and later with Family Tree DNA (FTDNA). Over the years I found a few interesting ways to relate matches to a side of the family. I tested both my father and his 1st cousin. They are both related on my father's father side . The benefits of this is that if there is a match with my father I always check the matches of his first cousin. If his first cousin also matches then the common ancestor is on my father's father side. if either my father or his 1st cousin do not match the the common ancestor is either on my father's mothers side or his first cousin's mothers side.
Another case I have tested my wife's half brother and am now in the process of testing my wife. They both share the same father. If a match is with one but not the other then the match is with their respective mother. If they both match then it is related to their father's line.
So if you have a family situation as this then, it is worth the cost of adding a cousin or a half sibling to your Autosomal DNA testing.
Also whenever doing a test always test the oldest possible tester that will achieve the desired results.
The reason I use FTDNA for all my DNA testing, is they are the only testing company that offers both Mt-DNA and Y-DNA testing in addition to Autosomal (Family Finder) testing. Family Tree DNA is having their annual Summer Sale presently and offers savings on bundles and single tests.
Richard Francis Pimentel
Lee, NH
Researching, Riberia Grande, Riberinha, Achada Grande, Bretanha, and Ponta Delgada, Sao Miguel, Acores