Linda,
I have been given to understand that Ancestry is the best route to go. You can download the DNA sample and transfer it for free to FTDNA and if you want the full benefits of FTDNA, it is a smaller fee than testing. You can then upload it to Gedmatch where you can match from all three.
Another route that is free is to sign up on Facebook for the Good Genes project. If you follow health stats enough (I think 2 days.), they give you an autosomal kit for nothing.
I have tested in all of these groups. I joined 23andMe and Genes for Good for purposes of trying to find a cure for my genetic disease that threatens to disable me and can be passed onto my children. They are the least useful for me. Genes for Good has been slow about providing results, while 23andMe keeps matches confidential, so you must rely on responses from the matches to get their data.
I like FTDNA but I hate their tree feature. They also have a chromosome browser. I tested there first, and it is where we tested the male Sinkey. My mtDNA test there was largely a waste, as mtDNA shows so few changes that you can match from thousands of years ago. I check these matches about once every 6 months.
My most useful DNA test has been Ancestry. You get lots of matches weekly, can match DNA to your tree, and download DNA to upload to Gedmatch. Ancestry does not provide all the tools that other folks do but Gedmatch helps here and is free. I tested Mom and my in-laws here too.
I too use GenomeMate, so I can help identify segments belonging to different ancestors. I just wish I had more time to learn more and work on it more. Facebook has some great groups that help: I follow Gedmatch, GenomeMate, and ISOGG.
Techteach