What I tell everyone is that there really is no reason not to test the entire mitrochondrial sequence. It isn't that long, and once you take an FGS test you won't have to take another -- at least, not for mtDNA.

In my case, when I first took the FGS at FTDNA, my haplogroup was H1. That's the same thing the 23andMe said, and the same thing that Ancestry said. However, later I ended up in H1bg. It wasn't because I took any more tests, but simply because the tree itself has been updated multiple times since I first tested.