"efficient tax system" is correct and usable in written English.
You can use it when referring to a system of taxation that is considered to be organized and effective in collecting revenue. For example, "The government recently introduced an efficient tax system to help raise money for public services."
It's the most efficient tax system in the world.
A more efficient tax system can mean more investment, bringing higher productivity and delivering that growth.
We can use it to advance a larger government, a more efficient tax system or some combination of the two.
The IFS added that independence would give Scotland an opportunity to design a "more efficient" tax system.
Yet Mr Camp and Mr Baucus have found enough common ground to build a more efficient tax system.
A more efficient tax system, even if it only raises the same amount of money, would likely increase revenues over time because you would get stronger GDP growth.
But their economic costs are held down by the perhaps surprisingly efficient tax systems with which they are financed.
Windfall revenues from foreign aid or natural resource exports can weaken governments' incentives to design or maintain efficient tax systems.
Scotland's Finance Secretary John Swinney said the ICAS analysis failed to take account of the "long term opportunities to create a modern, efficient and cost effective tax system in an independent Scotland".
Even if you think humanity should do absolutely nothing to stop global warming or reduce oil dependency, governments will want to spend money to handle the inevitable costs of warming or oil-dependence, and it would be far better to fund that spending with as efficient a tax system as possible.
In exchange for setting up companies in Estonia, e-residents can freely use some of the digital services that Estonian citizens already enjoy like the ability to register their company online, use e-banking to cover transactions, and a super efficient online tax system that reportedly takes about five minutes to file each year.
