It depends a bit on where you are, but there are few places where Ilford and Kodak materials are not obtainable.
If you use Ilford film, why not use their chemicals too? DD-X is expensive, but still only a fraction of the cost of the film you are developing. ID-11 is functionally identical to D76, and also an excellent developer. If you don't get good results with D76/ID-11 on Delta 400, you are expecting too much or doing something wrong. There is no magic bullet, so figure out what is bothering you and try to work on that. Of course, ask questions here if it will help.
Rodinal has never let me down, but you need to understand what it does, and what things it doesn't like. It needs very gentle agitation, not high temperature, and 1:50 dilution at least. Using it at 1:25 with rough and frequent agitation will never show you what it is capable of. At 22 deg C it produces noticeably more grain than at 20 deg C, and the theory is that 16 deg C is where it is actually best. I use it at 20, and accept the grain that it gives me. It is incredibly cheap and easy to make, too, as the Parodinal version. If I ever run into a developer crisis, I know my Parodinal is there to bail me out. And I'll print those negatives for anyone, anytime. It is a fantastic and convenient developer, used correctly.
All in all, I think the effort made to understand one developer and how to get the most from it is better invested than the effort spent in the hunt for the magic bullet. Whether that developer be HC-110, Rodinal, D76 or whatever else. If you ask 10 top-notch black and white photographers which film and developers they use, you'll probably get 10 different answers. But they'll all agree on this: Use what you have; understand what it does. I am fortunate to know one of the best printing experts in the world. He ran a black and white printing business for 40 years, and developed many famous photographers' films for them. I asked him what he used: D76 replenished, at 22 C and 8 minutes, regardless of which film it was. He can make a print from any negative that will blow your mind. He only uses Ilford paper and chemicals. Some photographers use TriX developed in D76, and nothing else, and produce results that are miles ahead of anything I can dream of. So, focus your energy on making good photographs, and use the Ilford (or Kodak) stuff as per instructions, and you will progress faster, IMHO.