I have a full node v 0.17.1 running 12-14 hrs/day and I was wondering if it's helpful, for privacy or for whatever reason, to add peers (maybe from https://bitnodes.earn.com/nodes/leaderboard/) with
Hardcoded peers are fine - the only time you would need to change them is if you worried they were in an entirely different set of peers from the rest of the Bitcoin network.
However, that is unlikely the case. They should have passed on their peers to you, so you can have an active connection with a much more diverse set of users in the network.
If you use
connect, you will only connect to those specific nodes.
addnode on the other hand tries to connect to the specified nodes, but keeps connecting to others as well (unless you add more nodes than there are outbound connections available, I presume).
It can be helpful regarding privacy to only connect to nodes you trust - how to find them is another question.
Also, there are no hardcoded peers in official bitcoin binaries as far as I know (check comments)
You can find bitcoin.conf example file here for more information.