You would get the 3x points per $ on both the taxes and the convenience fee (a lot of taxing authorities companies bill the convenience fee as a second charge. If the fee is 3% it isn't worth it unless you value Hilton points at over a penny and you KNOW you can use them right away. Hilton could very easily do another huge deval and/or the hotel you want to stay at may not have standard point rooms the date you want or change their category.

There is no way I would consider it on the Hilton Am Ex and the only way I would consider it on my Hilton reserve was if it would be enough to get me to the $10K spend for the free night and I was using it an expensive hotel.