Inability to see staff costs beforehand - staff is one of the 2 biggest expenses. I'm pretty sure the game works by having the default wages scale based on year, and on country. Showing the weightings for country in the country info page, next to the tax rate, would make a big difference. Pick a country to be 100%, and display the rest relative to that. Vanuatu's wages ingame are about 1/3 of the USA's, and that is making the difference between decent profit and steady losses.
I think staff pay rates are significantly more important than tax rates when it comes to picking a HQ.