STL vs xt vs whatever

Not sure what you mean by slicer, unless it's the program that generates the code for a 3D printer.  In all the 3D printers I have used over the years, STL has always been the file to use.  If there are other files types it'll accept, that is probably dependent on the program.  STL is like the standard so it'll be the one common type across any program.

I'm specifically talking about Slic3r Prusa Edition because that's what I use. It supports a number of formats like STL, OBJ, and AMF.

I'd just stick with STL as that is a universally supported and accepted standard file format for 3D printing.  OBJ is more for 3D graphics and computer rendering and so I've not found a major CAD package that supports it while most 3D graphics programs do.  I have not come across AMF.

If you are doing your own design then you can export a .STL, but sometimes if you are buying a model on-line it is in .OBJ  format.

Either one will work in most good slicer programs. And your design program can import an .obj and export it as a  .stl.

A slicer program is just taking your model, slicing it in in multiple vertical layers as oriented in your print with a thicknesses that your printer can print, say 25 microns, 50 microns or 100microns. 

Gotcha. Thanks for the replies guys. I just saw these other formats and thought maybe I was missing out on something better!