You should use the dynamic fee estimation feature of Bitcoin Core. When you go to send a transaction, there is an option at the bottom for "transaction fee" and a button labeled "Choose...". Click that and you will get a box with a bunch of information for setting the fee. Choose the radio button labeled "Recommended" and move the slider there all the way to the side labeled "Fast" (I think it is on the right, it may have been reversed). That will always set your transaction fee to be based upon what is currently happening on the network so that your transactions will have a (overly) sufficient fee.

There is one caveat though. You need to have Bitcoin Core running a for a while in order for it to gather enough data to properly estimate the fee. So you cannot just start Bitcoin Core and expect the fee estimator to work but rather keep Bitcoin Core running for a while before you send.