Currently, there are primarily the big three companies doing DNA testing -- 23andMe, FTDNA, and AncestryDNA. 23andMe and AncestryDNA each offer a single test, while FTDNA offers several. Kit costs can vary by country, shipping costs can vary widely by company to country, and the tests aren't available in some countries, although more are being added over time. AncestryDNA also requires an ongoing ancestry.com subscription for new tests to take advantage of all features.
As to Y-DNA, only FTDNA's Y-DNA STR test results are truly compatible with RM7. The 23andMe test looks at Y-DNA SNPs, while the AncestryDNA test only includes a more limited number of Y-DNA SNPs in its raw data download file. 23andMe actually provides a paternal haplogroup based upon the Y-DNA SNPs it tests, so I suppose that you could enter that haplogroup in the Y-DNA fact and leave many of the other fields within it empty.
Y-DNA STRs only serve to estimate broadly a paternal haplogroup, but SNPs are needed to validate/determine it. FTDNA also has what's called the Big Y that tests the most Y-DNA SNPs of any tests from the three companies. It's also fairly expensive. FTDNA offers individual SNP testing a la carte, as well.
FTDNA's mtDNA test includes one for all SNPs within the HVR1+2 regions and another for all within the HVR1+2+3 regions. 23andMe's test looks at just a subset of the mtDNA SNPs throughout all three, so isn't the best option since you enter those SNPs that differ from the "reference" for each region, so can be misleading. AncestryDNA's test doesn't look at mtDNA at all. Again with 23andMe, you could enter your maternal haplogroup assignment into the RM7 DNA fact.
All three companies test autosomal DNA (chromosomes 1-22), which is better suited for determining ancestry in more recent ancestry. The FTDNA test that does so is called Family Finder. That test is different than its Y-DNA and mtDNA tests given above, and the FF test doesn't look at Y-DNA or mtDNA. If you're serious about your more recent vs. deep ancestry, these atDNA tests are the ones that you'll want to purchase, but the problem is that the results aren't suitable for input into RM or other genealogical packages since so many more markers (many hundreds of thousands) are tested.
Finally, Y-DNA is passed down without recombination from father to son (except for a very small amount), so traces the deep ancestry along your direct paternal (father's father's . . . father's) line. mtDNA is passed without recombination from mother to child, so traces the deep ancestry along your direct maternal (mother's mother's . . . mother's) line. atDNA is passed down with recombination from both parents, so traces the more recent ancestry along all the lines along both your paternal and maternal sides. After several generations, atDNA from a particular ancestor may no longer be evident due to recombination. (The X-DNA inheritance pattern is more complex, so I won't include it here.)
As to the autosomal tests, each of the companies has its advantages and disadvantages, but if you can afford to test at all three in order to expand your possibilities for matches, I'd recommend it. FTDNA allows autosomal raw data transfers from 23andMe and AncestryDNA to its FF product for a reduced fee. However, the 23andMe data has to be from v3 of its chip, and new tests are on v4. It's probably most cost effective to test at 23andMe and AncestryDNA and transfer the AncestryDNA raw data to FTDNA FF.
I'd probably not recommend the FTDNA Y-DNA STR or mtDNA tests unless you're unsure of your surname (adoption or non-paternal event along your direct paternal line or direct maternal line). If you don't have uncertainties, the haplogroups provided by 23andMe may be good enough in order to disprove a hypothesized relationship along the direct paternal line and direct maternal line. Even if there are uncertainties about your direct maternal line, a FTDNA mtDNA test seems to be much less useful since a woman's surname changes each generation and surnames are less commonly given going back in time.
Genetic genealogy is much more difficult than the companies would have you believe, so be sure to keep expectations low and realize that it's a long-term pursuit. As more people continue to test, you'll have a better chance of finding more and closer relatives.
If considering testing soon, you might wait to see if any promotions are announced for National DNA Day (25 Apr 2015). FTDNA often puts Y-DNA STR tests on sale over Father's Day (USA date) and mtDNA tests on sale over Mother's Day (USA date). You may also see sales around the Holidays.
