Since you are starting out, and the 45LC is a deep cartridge, use Trail Boss. It is a new, bulky powder especially designed for light loads in large cartridges, and is not position sensitive.
In comparison, you would have a hard time seeing a few grains of Tight Group or Clays in the bottom of a 45LC case.
Trail Boss is a few dollars a pound more expensive, but still worthwhile for at least your first pound of powder when you are starting out. It will give you a much better level of confidence being able to see if you have accidentally double charged a case. (BTW, this is my standard recommendation for new reloaders of handgun cartridges. The bulky powder makes it so you have less thing to worry about)
After you get the hang of reloading, you will find Tightgroup very versatile and Clays to be very clean.
