Every company has a slightly different offering (and price!) and it’s important to review these when deciding which test to take. In addition, it’s important to consider which DNA tests can be downloaded from the testing site, and which other sites will allow them to be uploaded.
The commercial DNA test available from almost all Genealogy Companies is the Autosomal (atDNA) test. This means that they look at the DNA contribution from all our most recent ancestors with no differentiation as to who those ancestors are. If we want to differentiate between the ancestors on our paternal and maternal sides, we need to get our parents, or our parent’s full siblings, to take their own tests and cross-reference those results with our own.
LivingDNA (as used by FindMyPast) and FamilyTreeDNA both offer matches based on Y Chromosome (Y-DNA) and Mitrochondrial (mtDNA) testing. That is, identifying which matches come from our exclusively male (father-son) or exclusively female (mother-daughter) lines. FamilyTreeDNA also offers matches based on X Chromosome (X-DNA) testing.
X-Chromosome testing is done by default as part of the Autosomal test, but it can also be tested independently to identify relations through a particular ancestral line in our DNA. However unlike Y-DNA and mtDNA, where we can clearly identify the ancestral path as being the exclusively male and exclusively female lines respectively, the X-Chromosome is passed down through unpredicable paths in our ancestry with no way to specify which particular ancestors it came from. A man (YX sex Chromosomes) inherits his X-Chromosome from his mother’s line. A woman (XX sex Chromosomes) receives one X-Chromosome from her father’s line, the other from her mother’s.
23andMe also provides Y-DNA and mtDNA testing, but its DNA matches are all made through Autosomal matching. There is no differentiation for Y-DNA or mtDNA matches.
FamilyTreeDNA is the most inclusive choice for DNA testing, therefore. However, the problem is that our list of matches is only as good as the pool of DNA samples against which our own DNA test is being compared. And, at present, the pool of DNA samples held by FamilyTreeDNA is dwarfed by that held by other companies.
My recommendation, therefore, if your focus is family history research and if you want to find long lost relatives, is to use AncestryDNA. This benefits from a massive database of more than 10 million users as well as the extensive resources of its genealogy website. At the moment there is no way to cross reference DNA results with a Family Tree on FindMyPast. MyHeritage does provide this facility but, in my opinion, lacks the user-friendliness of Ancestry in this regard. In addition, though AncestryDNA will not accept tests done on other sites, it will upload to pretty much any other site providing Autosomal testing. In this way your AncestryDNA results can also be put onto FindMyPast, MyHeritage etc. and you only pay to be tested once!