Congratulations for having such a choice. Kudos to your employer.

If I do not take into account taxes, I'd decide based on how much effort you want to invest into dealing with your money. If you do % split fiat vs btc, then you are worry free and no need to try to find p2p people etc. etc. And your % in fiat could just be the bare minimum you need to live on + 10% for some unforseen circumstances.

If you have plenty of time on your hands to monitor the market and want to be more hands on, then getting paid in FIAT and DCAing during the dips is could be more profitable.