Should I make one large bird or 2 smaller ones?
Depends on the size of your oven. If you can cook 2 small turkeys they will cook faster than one very large one
A larger bird might be a better choice for a large crowd, 2 small turkeys might go quickly and then there might not be enough to go around.
How many people are in your crowd?
One bird per oven. If you have two ovens ...
Small birds have more bone, less meat, proportionately if that helps.
A big turkey takes a long time. Find out how many are coming and then use this formula 3/4 to 1 lb. of turkey per person. The bones, like someone said get in the way of this formula for smaller crowds. I would not bother to cook less than a twelve pound turkey on Thanksgiving, and Pleasantville Turkeys, half turkey, about 7 lbs. serves only 3-4 hungry people at my house. The most efficient way to have enough turkey is to cook a 14-16 pound turkey and put a small boneless turkey breast into the pan at the appropriate time to get it done. It will fit in the pan if you don't use the roasting rack. The flavors of the roasting meat will make it super good, and no one will be the wiser that gets the extra turkey. Those white meat breasts go really far. But if you have the time and the oven space, the larger 25 lb. turkeys are really impressive. You need to make sure you have someone who can lift them out of the oven and out of the pan. Just cool it a bit before you try removing it from the pan so no one is burned by hot grease.