Dogecoin has only one advantage: Elon Musk tweeting. If Elon Musk loses interest in Dogecoin so will everyone else. Cardano on the other hand has a whole team dedicated to marketing Cardano and improving it.
Dogecoin is not a serious investment. The developers themselves will admit it was created as a joke. It will be around but I doubt it will ever be taken seriously even if Elon claims to "fix it". It is a meme coin and thats what it will forever be. I mean can you imagine actually being paid in a Dogecoin?
Cardano on the other hand claims to offer something in terms of usecase but it too seems like vaporware at the moment. Nothing actually runs on Cardano. But if I had to pick for the mid-long term. I would go with Cardano. Simply because its not a meme.