I would say Bitcoin Core is the most secure Bitcoin wallet , But it have a lot less feature then the other wallets like importing & exporting private keys & it also download the blockchain file which is big & takes time to do it .
What do you mean?
With Bitcoin core, you can import and export private keys easily. And yes, you will need to have atleast ~30+ GB to run Bitcoin core but this will be fixed with the upcoming long waited update.
If you can afford buying Trezor , just do it ! It is the most secure in my opinion.
You are right. If you can't buy Trezor, you can buy BTChip or Legder wallet. It is cheaper but secure like Trezor but have lower physical security.
If not , and you insist using Desktop wallets , then just go with Electrum , pretty easy to use & you can recover your wallet in case of failure in your computer with 12 words seed
You can also use Multibit-HD or Multibit instead of Electrum.
~~MZ~~