The most inline with Bitcoin design would be the Mimblewimble chain format because, unlike other designs discussed in this thread, it achieves better privacy by making the protocol simpler. It also comes with the simplest onchain mixer which, as far as I know, is much more efficient than any mixer on Bitcoin.
I don't think Monero's ring sigs are worth considering at this point. The idea was very interesting years ago, but at least to me, it seems like a relatively bad tradeoff to make today. You're much better off adopting ZCash's newest z2z variant or something like a variant of Lelantus.