This is like discussing the difference between a Toyota Camry and a Toyota Corolla. Either is suitable and the differences between the two are quite limited. They are both Opioid agonists, i.e. they are what you want. Dihydrocodeine is generally twice as potent as Codeine, however this is going to vary greatly from person to person, as the action of both of these drugs is dependent upon the enzyme activity inside your body. If you are a poor metabolizer, you will ultimately convert less Codeine -> Morphine.
Dihydrocodeine is metabolized in vivo to Dihydromorphine. As I said, it's typically twice as potent and seeing as how you already have experience with Codeine-based substances, I would say you have a reasonable benchmark from which to predict your outcome with the DHC.