I do, I'm a biased opinion, that said, I think characteristically it breaks down like this:
Alias best DVD's show the most advanced techniques and there for are hardest to follow (Still excellent DVD's), the more intermediate and beginner of Alias's DVD's I'm not as familiar with.
Gnomon are good beginner to advanced, but breaks it into a lot of DVD's to cover all that info, and has a lot of diverse, knowledgeable on the specific topic, artist help to create them.
Digital tutors is good for beginner to advanced focusing on beginner to intermediate or that's where most of their DVD's are. The positives to DT are that it's clear on the topic and to the point, you get a lot out of each DVD on a broad topic. Where as Gnomon gives you a lot out of each DVD on a more focused topic. Again I'm trying to generalize, so not always the case.
If money isn't an issue (like if you can request that your company buy them) I sugesst getting them all (ALias, Gnomon, DT) on the topics that interest you. They are all worth more in knowledge than they cost. There are no worthless DVD in any of them that I've seen so far.
And if it's your money and you can only afford one I'd say assess your knowlage and pick which DVD would help you the most, according to it's list of topics. Like if you are new to a topic, and don't have a lot to spend then maybe DT would be best for a beginner overview, if you know some and want to know a lot about something specific like how to use springs them Gnomon would be a good choice. They really are all good DVD's. I've gotten the company I work for to buy extensively on the topics that interest me, from each company.
I love learning from the DVD's it so much better than books.
Hope that helps.