So my question is, apart from electrum wallet which other wallet is the safest for long term holding of bitcoin?.
It may worth mentioning that electrum can give you complete security, only if you run it on an airgepped device.
If you run electrum on an online device, there's always the chance of getting hacked.
If you want to be completely secure and you can't have an airgapped device for any reason, you should go for a good hardware wallet. That's the only option for you.
Beside Electrum wallet, you can use Bitcoin Core, full node if you want best privacy with Tor connection, or prune node if you are not serious about privacy.
Whether you a run a prune node or you keep the entire blockchain, it has nothing to do with level of privacy.
Even if you run a prune node, you can still broadcast your transactions by yourself without relying on any third party.