The topic of entropy is interesting. If I were to pick one, I would probably test the dice statistically and then use that. Computer RNG? Could have been compromised by any number of parties (e.g. the CPU manufacturer). The idea of combining the two is to have some safety in the very unlikely case my dice throws are getting messed up in some unimaginable ways.
Does it really matter?
Let's say your "computer RNG is compromised", whatever it means for you. Finally all you have is private key and address. Do you think someone will try to attack your coins assuming that you used compromised RNG when you generated your seed?
I have a feeling that you want to play with all that just for fun, not because of any real issue.
Even if you use a coin for your flips, it could be not balanced. I everyone would know that coins X are not balanced and ratio is not 50/50 but let's say 51/49 - do you think your seed is not secure?
Anyway, at the end you may always verify if your result is "random enough". I wanted to attach famous strip of RNG "999", but it is part of that page:
https://www.incibe-cert.es/en/blog/verifying-randomness together with some links to very interesting papers.