If you want to elminate the saturated fat, which butter, shortening, and lard contain, just give plain old vegetable oil a try. It sure can't hurt anything just giving it a try.
A while back my wife decided that she wanted to make some tamales from scratch. Well all the recipes we could find called for lard. She didn't want to use lard, so she just used canola oil instead. We weren't sure how it would work, but the tamales came out fine and tasted great! So, just because a recipe calls for a certain ingredient, don't be afraid to experiment a bit. If it doesn't work, then just mark it up to experience.