Tomorrow is Thanksgiving, and the city’s proposed ban on trans fat is looming. So it is a good time to ask: How will this affect the pie? Though the city council’s proposed ban, which may be revised next month, wouldn’t affect home cooks, it’s an impetus to assess the relative merits of the partially hydrogenated foods.

Since shortening was commercialized into the American diet nearly a century ago, everyday pastry makers have been folding cold lumps of the creamy white fat into flour in search of the perfect crust. Nearly every pie crust recipe today calls for at least a quarter of the fat to be shortening. Conventional wisdom has it that shortening is what makes crust crispy and flaky.

So during this important pie season, I held a pie crust blind taste test to find out which fat makes the best feast. The test: four everyday fats available at neighborhood grocers. Then I rounded up a few pie-loving friends. By no means was this experiment scientific. It just involved an avid cook and a few friends using a modest kitchen the way millions of Americans will in the next two days.

There are many options for pie crust fats. Beyond butter and the country’s standard trans fat — Crisco — there is a non-trans fat Crisco, oils, and animal fat options that include duck fat and fresh lard. The latter has very little trans fat, but because of its shorter shelf life, it is harder to find than the processed lard available at grocery stores and corner bodegas.

I settled on four pies that would give a range of taste and flakiness: all-butter, all-Crisco, all non-trans fat Crisco, and all-homemade lard. (Most pies have a combination of about four tablespoons of shortening or lard and 12 tablespoons of butter.)

For the crust and filling, I consulted “The Gourmet Cookbook,” settling on the American standard: apple pie. For the taste test, I attached colored stickers to each 9-inch pie pan: green for butter, red for regular Crisco, yellow for lard, and blue for non-trans fat Crisco. Only the photographer and I knew the scheme.

Rolling out the two shortening pies was a much tougher task than the butter pie, which smoothly formed a disc and was easier to assemble when pinching the crust together.

Tasters preferred the Crisco crust over the non-trans fat Crisco, calling it a little flakier with a more appealing taste. But the two were so close that, when asked to weigh the health risk, “the difference wasn’t enough for me,” taster Devin Gaffney said.

The lard had a smoother texture, a healthier look, and held up better against the fork, but the flavor was off-putting to two of the three tasters. As the lard pie baked, the room filled with the aroma of rendered fat, like a slow-cooking pork roast mixed with the sweet smell of melting sugar and cinnamon crusted apple. The all-lard left at least one of the tasters a little disappointed.

“I thought I would like the lard the best,” taster Garrett Fennelly said.

But shockingly to all of us except Mr. Gaffney, it was the all-butter pie that was the overall favorite. Besides the creamy butter flavor, the crust was light and flaky and crumbled easily under the weight of a fork.

“I knew I would like the all-butter pie best,” Mr. Gaffney said.

“In the end I want a crumb with more flavor,” taster David Cross said.

Where the butter didn’t do well was in the hours and days it sat in the refrigerator with the other pies. By the next morning, the butter pie had become moist, losing its crumble and flakiness.

The lard and two shortening pies had done a better job of keeping their texture, and by the end of the weekend it was the lard pie my roommates had devoured.

I took a fork to the remaining pies and found the all-butter crust had completely crumbled, while the two shortening pies were still flaky. The cool refrigerator and age did nothing to break down their hydrogenated fatty walls.

So if you’re eating the whole pie tomorrow, butter is best. It’s fine for Thanksgiving — just make sure there aren’t any leftovers.