Let's take it from the back end:
The last 2 are tiled for you to print on either ANSI A(letter) or B (Tabloid) size paper, depending on what printer(s) you have access to or if you use a print shop for it, and subsequently glue or tape together. ANSI B will naturally make this simpler and faster. 8½x11 is ANSI A, which is the one you should pick for printing.
The "Full Size" is an untiled plan, great for getting an overview - I'd keep a copy of this one on the PC for help during drawing assembly as well as checking stuff that might not be on the pages printed, or lost in assembling the drawing or whatever. It's also the one to get if you want to rezise the plans, like I do for 6mm Depron building.
The top one just called "FT Simple Cub" is a "One-stop-all-variants-included" with both the untiled and ANSI A an B Tiled plans included (same plan 3 times in one file).
