I will say, Adagio's samples come in adorable little tins. So cute. And so practical...mine quickly disappeared as I used them as containers as I gave little batches of other teas out to people as gift samples.
Adagio is a good company to order samples from. Another, which has a massive catalogue, more variability in quality (more "misses" than Adagio, IMHO, but perhaps, slightly better prices on average) is Upton Tea Imports. And I do think black teas are their strength, whereas Adagio, I think is a little more of a well-rounded company. And Upton has fantastic prices on their samples...many of them are $1 for 15 grams...you can't beat that. They do not, unfortunately, come in cute tins. Upton does have samplers that come in tins...but...I just...I don't like the shape of the tins as much as Adagio's tins...Upton's are flatter and round...I like how Adagio's are more squarish and deep...much more practical.
So order from Adagio first, get the tins, then order from Upton...haha.
But...seriously. Also...Rishi has some good black teas. Their samples are a bit larger (1 ounce size) which you may or may not like...and they're pricier, both because their prices tend to be higher b/c of fair trade + organic status, but also because of the larger size. But I still would recommend them, I've had very good experiences with Rishi's black teas. Not the hugest selection, but a good selection.