Electrum of course without any doubt. Many would argue that bitcoin core is the best but electrum is go to WALLET for even grannies. I would recommend electrum to my grannies too.
The P2SH addresses are not truly segwit but a compatible address which can receive bitcoin from segwit, legacy and its own addresses.
Native segwit, nested segwit, legacy all of them are compatible for receiving and sending bitcoin to each other. Your post is kind of confusing, may be only to me. You said as if segwit can't receive btc from legacy and vice versa while it is not.
I have tried an exchange before using legacy address, the transaction was reversed back into the wallet two times until I used legacy address. But I have indirectly made a comment about it in the bitcoin technical support today and I was corrected.