Between mobile and a desktop wallet which one do you prefer the most and why? Again I think desktop wallets have more open source wallets than mobile, which desktop wallet is the best open-source wallet that you know of?
It depends on the nature of your needs.
I mean, what currencies do you intend to store? And how do you intend to use it?
If you intend to store bitcoins, for example, I advise you to use the Electrum wallet in the desktop version and the mobile version for daily use of small payments.
For the rest of the cryptocurrencies, I advise you to use the official wallet for each currency and avoid multi-currency wallets because they are necessarily central wallets.