There is still a lot of gaps in both of their campaigns, but we now have enough to start comparing. I tried to find the most non-partisan links possible.

Harris:
Exempt tip income from taxation. Read more
Expand the child tax credit to $6,000 for children under age 1, $3,600 for children 2-5, and $3,000 for older children. Read more
Expand the earned income tax credit for filers who do not claim children. Read more
Expand premium tax credits. Read more
Expand housing tax credits, including the low-income housing tax credit, a credit for new homebuyers, and a credit for the construction of started homes. Read more
Claw back deductions for depreciation and interest for certain rental construction investment. Read more
Exempt tips from the income tax. Read more
Expand the child tax credit to $6,000 for children under age 1, $3,600 for children 2-5, and $3,000 for older children. Read more
Expand the earned income tax credit for filers who do not claim children. Read more
Expand premium tax credits. Read more
Expand housing tax credits, including the low-income housing tax credit, a credit for new homebuyers, and a credit for the construction of started homes. Read more

Trump:
Lower the corporate income tax rate from 21 percent to 20 percent. Read more
VP candidate JD Vance has discussed increasing the child tax credit to $5,000. Read more
Make the expiring estate tax cuts from the 2017 Tax Cuts and Jobs Act permanent. Read more
Make the expiring individual income tax cuts from the 2017 Tax Cuts and Jobs Act permanent. Read more
Consider replacing personal income taxes with increased tariffs. Read more
Exempt tips from income taxes. In 2018, IRS W-2 data indicates 6.1 million taxpayers reported a total of $38.3 billion in taxable tip income, for an average of $6,249 per taxpayer. Read more
Exempt Social Security benefits from taxation. Read more
Impose a universal baseline tariff on all US imports of 10 percent to 20 percent. Read more
Impose a 60 percent tariff on all US imports from China. Read more
Consider replacing personal income taxes with increased tariffs. Read more

Digging under the hood, I would say that the biggest differences would be tariffs and Trump's tax cuts.
As for tariffs, I kind of lean towards the baseline 10% rate. However, the 60% on China is extreme.

A worldwide 10 percent tariff and a 60 percent tariff on Chinese goods proposed by Republican presidential candidate Donald Trump would lower average after-tax incomes of US households in 2025 by about $1,800, or 1.8 percent, according to a new analysis by the Tax Policy Center. They’d reduce imports into the US by about $5.5 trillion, or 15 percent, from 2025–2034...
All income groups would see similar percentage declines in after-tax income as a result of Trump’s tariffs, ranging from 1.7 percent to 1.9 percent, TPC estimated. The biggest exception: Those with the highest incomes, whose after-tax incomes would fall by about 1.4 percent.

As for Trump's taxes, that's already well known.

Households with incomes in the top 1 percent will receive an average tax cut of more than $60,000 in 2025, compared to an average tax cut of less than $500 for households in the bottom 60 percent, according to the Tax Policy Center (TPC).[1] As a share of after-tax income, tax cuts at the top — for both households in the top 1 percent and the top 5 percent — are more than triple the total value of the tax cuts received for people with incomes in the bottom 60 percent.
The Congressional Budget Office (CBO) estimated in 2018 that the 2017 law would cost $1.9 trillion over ten years,[3] and recent estimates show that making the law’s temporary individual income and estate tax cuts permanent would cost another roughly $400 billion a year beginning in 2027.[4] Together with the 2001 and 2003 tax cuts enacted under President Bush (most of which were made permanent in 2012), the law has severely eroded our country’s revenue base. Revenue as a share of GDP has fallen from about 19.5 percent in the years immediately preceding the Bush tax cuts to just 16.3 percent in the years immediately following the Trump tax cuts, with revenues expected to rise to an annual average of 16.9 percent of GDP in 2018-2026 (excluding pandemic years), according to CBO. This is simply not enough revenue given the nation’s investment needs and our commitments to Social Security and health coverage.

Finally, there's Project 2025. How much that would impact Trump's policies is hard to say, but it's not hard to say that it would have some impact.

Currently, there are seven tax brackets — 10%, 12%, 22%, 24%, 32%, 35% and 37% — with each based on income thresholds. For instance, a married couple pays 10% in federal income tax on their first $23,200 of income, and then 12% on earnings from $23,201 to $94,300, and so on. Married couples need to earn over $487,450 this year to hit the top tax rate of 37%.

Project 2025 argues that the current tax system is too complicated and expensive for taxpayers to navigate. To remedy those problems, it proposes just two tax rates: a 15% flat tax for people earning up to about $168,000, and a 30% income tax for people earning above that, according to the document. It also proposes eliminating "most deductions, credits and exclusions," although the blueprint doesn't specify which ones would go and which would stay.

He estimated that a middle-class family with two children and an annual income of $100,000 would pay $2,600 in additional federal income tax if they faced a 15% flat tax on their income due to the loss of the 10% and 12% tax brackets. If the Child Tax Credit were also eliminated, they would pay an additional $6,600 compared with today's tax system, Duke said.

By comparison, a married couple with two children and earnings of $5 million a year would enjoy a $325,000 tax cut, he estimated.

"That 15% bracket is a very big deal in terms of raising taxes on middle-class families," Duke said.

Millions of U.S. households earning less than $168,000 would likely face higher taxes with a 15% rate. Currently, the bottom half of American taxpayers, who earn less than $46,000 a year, pay an effective tax rate of 3.3% — which reflects their income taxes after deductions, tax credits and other benefits.