I've had 2 different tests done. FTDNA and Ancestry. I did the basic Ancestry test second because I realized that their resources are far more vast. It was a great way to confirm blood lines that were, until then, largely educated guesswork. I mean, it's pretty cool when you see that you share a 6th great grandparent with somebody and that's confirmed by DNA because that goes way back. Yes, there are concerns about privacy, but I don't really give a crap. I had uploaded stuff to gedmatch, but that really is a pretty limited service and most of the folks on it don't even have trees or have shitty ones with like 4 people.
You can find a lot of cool shit on Ancestry, but it really is a rabbit hole that you will find yourself spending hours on if you aren't careful. So much info to be had and you find yourself spinning theories about people you've never met. I've been quite fortunate, though, in being able to trace both my parents' lines back to the era of Scottish kings. There are all sorts of interesting and unsavory characters in my bloodline, and also quite a few literal saints. I think the furthest back I've been able to go is the 500s on dad's side and the 800s on mom's, but it isn't like I share that DNA anymore. This is also a pretty uncommon experience in my understanding.
Weird story...there are a few branches that are dead ends, but by and large I've been able to trace pretty much all the lines back to colonial times. One of my Irish lines has been enormously tough because they came over here, lived shitty lives, and basically all died young and potato famine records in Ireland are for shit. So in trying to find DNA confirmation for that line, I stumbled on one guy who basically couldn't be related in any way except that Irish line. I look at the tree, send an e-mail, and of course don't hear back, which isn't uncommon. But then I'm looking at the e-mail and the name on it is familiar. I hit up his Wikipedia page and confirm some of the names that are matches on this tree. These aren't common names either, so I'm thinking holy shit. Anyway, long story short but looks like I'm related to Jimmy Kimmell. Fucker needs to answer his e-mail. He has the resources to plug holes in that Irish line.