Monero
Mimblewimble has privacy features, but it also has the first really impressive, true scaling solution in crypto. Privacy-wise, Monero is probably better overall, but its scaling is abysmal, and neither coin can be treated as an impenetrable black box.
Grin has succeeding in reducing the size of the blockchain. However, it's
still limited to 10 TPS, so the more significant scaling problem remains.
With it's adaptive blocksize,
Monero can process >10 TPS (up to 1,700 theoretically).