I'm not a math expert, but I filed my own taxes for many years. From my understanding, Here's the math if value of the stuff is $100. So, donation value is $100 - that means you can write off $100 of your income. If you are in the 15% tax bracket, you save $15 in taxes. If you are in the 20% tax bracket, you save $20. So, if you can sell an item that's worth $100 for more than $20 through Craigslist, that is financially better. If you are in a different tax bracket, you can adjust accordingly.
This doesn't include any valuation of the cost of your time.
Personally, I gave the bigger baby stuff one shot on Craigslist for a reasonable price and make it clear in the ad that it was a firm price. If no one responded in a week or two, I donated it.
ETA: MilitaryMom6 is correct that my math assumes that you itemize your taxes instead of taking the standard deduction. If you don't itemize (file schedule A), then you get nothing for donations at tax time.