There are plenty of other states with more favorable tax laws than Delaware. Delaware is popular because of it's well developed corporate caselaw and unmatched judicial experience, which is particularly attractive to investors (i.e. potential plaintiffs) because it minimizes legal risk.
If you want investment, there are only two states to consider when incorporating: your home state or Delaware. Any other state will give investors and their legal counsel pause.
That's not quite true. States do specialize, for example Nevada is known for those seeking beneficial living trusts, Montana is known for holding companies for expensive motor vehicles, and so on.
There is a large body of research and a wide variety of actors across the political spectrum who are all in agreement that the US is one the largest tax havens in the world. I can only assume that you've never been exposed to any of that and are simply making a knee-jerk reaction comment.
There are many, many more such things written over decades. Here's a 2009 article from The Economist on the same subject of America's status as one of the world's premiere tax havens: http://www.economist.com/node/13382279
You're technically correct, the best kind of correct.
Most countries around the world have higher effective tax rates than the US, and this was true even before the tax cuts. (People who claim otherwise are citing flawed political studies that ignore how tax deductions and credits are actually used by companies, and the ultimate average corporate tax burden. Even in industries subject to high effective rates, like retail, they still pay lower effective tax rates than their Euro counterparts. If they're not, they need to hire better accountants.)
The US is also the premiere information disclosure haven in the world...as long as you're comfortable sharing your info with the US government. We require most other countries to share financial information with us but we don't return the favor.
But the fact of the matter is that the US is not an actual tax haven. We impose taxes and enforce tax collections. There are real tax havens, like the Isle of Man or the Cayman Islands, which don't have taxes and which have legal entity laws that promote tax-shelter holding companies.
If you want investment, there are only two states to consider when incorporating: your home state or Delaware. Any other state will give investors and their legal counsel pause.