Which is more profitable: an assignment or a double close, and why?

If syndicator is building reserves for the first year of ownership, for instance, and not paying distributions, AND recognizes rental profit, you will have a larger tax bill that year, since you "made money" in the IRS's eyes, even though you did not receive any cashflow from your syndicator.On a more general note, a preferred return does not mean you will get that amount of cash flow each year.  

Diving deeper.. check who’s on their team, how they structure their deals, and whether you’re comfortable with how the profit splits work.

What this implies to the typical RE investor is obtaining significant cash flow is a big challenge right now and relying on other RE profit sources (such as a value add and not doing a value subtract) may be a more certain path of generating returns.  

If you already have that where you live, why put those profits at risk?

While not impossible, you'll be paying a much higher interest rate for the loan than with 20%+ down and also you're likely paying some points or splitting the profit if for resale. 

It's not that challenging to get above a 10% return in real estate with all of the profit levers (cash flow, appreciation, mortgage paydown, tax benefits, leverage)?

If they talk about "halting distributions" to investors to focus on future business growth and profitability, what is their actual business plan?

Following the shiny object, throwing money at a market you don't know well, and blindly trusting strangers that have a clear profit motive put you in a poor position to succeed regardless of where you choose to invest.

There are companies who buy properties and flip them for large profits each month.