Let's take the Bush tax cuts for example... $300.00 or $600.00 per couple. What did I do with my $300... I paid off a credit card and then closed it. That did nothing for the economy... What did my parents do with their $600.00.. they put an extra payment on the house... which did nothing for the economy. But what did my friends who were just making ends meet do? They went out, and bought food, and an Xbox to provide the family with entertainment. I didn't adjust my spending habits at all, but they did and bought a luxury and therefore stimulated the economy. So it would have been better stimulus, to give me and those who make an income higher than me nothing and double or triple my friend's tax cut. OR as many poor people don't make enough to pay any taxes, perhaps double their food stamp allowance, or increase the earned income tax credit, or... I could go on. The point is tax cuts for the rich are of limited stimulative effect.
Pivoting to direct government investment. When the government pumps money into an economy directly it had multiple benefits. Large government infrastructure investments employ people... the workers, the suppliers, the food vendors nearby... and allow for greater economic activity. Adding light rail between Seattle and Tacoma will increase the flow of people and therefore the flow of money. Adding lanes to I-5, finishing 167 or the cross-base highway will allow goods and services to flow more effectively across the region. Paying states not to lay off teachers will have the net benefit of smaller class sizes, improved education (which will pay long term benefits), and oh yeah, keeping a skilled and specialized workforce employed and spending money. The benefits of direct government spending are large, but hidden. How do you know the state worker who lives next door to you kept his job due to the stimulus? But you do see that $300.00 that you ended up using to pay off that credit card. Tell me, what has a higher long term economic benefit.. a $40,000 a year job as a teacher... or $300?
Tax cuts to billionaires will go into savings accounts, or hopefully stock portfolios to increase capital available for investment, but we really can't say because as a society we have no control over what people will do with that money. Additionally, there is a lag time. You can cut taxes, but it will take people a while to realize they have more money and spend. A $1,000 a year tax cut comes down to an extra 83.00 a month... what will you use it for? Will you even notice?