With the current volume of unconfirmed transactions and the increasing transaction fees it is sometimes difficult to determine the required transaction fee. If you use the default value of your wallet your bitcoins may be locked up in an unconfirmed transaction for several weeks. In order to determine the required transaction fee you need to know the transaction fees that are currently required by the miners. I found a nice site that gives a very clear picture of the transaction fees that are currently mined and the transaction fees that are pending in the bitcoin mempool: https://dedi.jochen-hoenicke.de/queue/#24h
The picture for the current week is as follows:
You can also see the weekly trend in the transaction fees on this site. If you can you should wait until Sunday evening because the trend has always been that the lowest transaction fees are paid on Sunday night. In the most recent graph you can see that currently the fees are 140-200 Satoshi per byte. I expect the fees to go down during the night so 150 Satoshi per byte should be ok for an overnight confirmation. If you want to be 99% sure you should pay 250!