Insulation troubles

Hey guys,
I am finally ready for floor insulation. I am at the big box store but I gotta tell ya, they ain't got much!! All they have are basically three types. There is one called r max tmatte plus-3 that looks like actual foam with a foil back. It says it's r value is only 2.9. Then they got the blue styrofoam that's Dow branded says it has 3.0 r value. Then they got something called polyshield styrofoam sheathing underlayment that looks like white styrofoam with a paper front and foil back. Says is 2.9. All of these I am not sure about. Here is another thing. The only one they have in 3/4 is the polyshield I believe. The depth of my "hole" where I am putting my I insulation is roughly 1 1/2 inches. Am I supposed to double up panels to get it flush or just put one panel in and leave open space? Can someone gimme a hand? Oh yeah. This is an open floor deal. No sandwhich. It's like what the gen ben plans refer to.
EDIT- So the other big box orange store on the other side of town has this stuff. It has a higher R value and I see a lot of the others using the "pink" stuff. This looks to come in 1" and 2". If I went with this stuff...would it be better to get the 1" and it not be flush to the bottom or get the 2" and have it sticking out?? I suppose it could be cut some way to make it less than 2" but that would be a real PIA.
I am finally ready for floor insulation. I am at the big box store but I gotta tell ya, they ain't got much!! All they have are basically three types. There is one called r max tmatte plus-3 that looks like actual foam with a foil back. It says it's r value is only 2.9. Then they got the blue styrofoam that's Dow branded says it has 3.0 r value. Then they got something called polyshield styrofoam sheathing underlayment that looks like white styrofoam with a paper front and foil back. Says is 2.9. All of these I am not sure about. Here is another thing. The only one they have in 3/4 is the polyshield I believe. The depth of my "hole" where I am putting my I insulation is roughly 1 1/2 inches. Am I supposed to double up panels to get it flush or just put one panel in and leave open space? Can someone gimme a hand? Oh yeah. This is an open floor deal. No sandwhich. It's like what the gen ben plans refer to.
EDIT- So the other big box orange store on the other side of town has this stuff. It has a higher R value and I see a lot of the others using the "pink" stuff. This looks to come in 1" and 2". If I went with this stuff...would it be better to get the 1" and it not be flush to the bottom or get the 2" and have it sticking out?? I suppose it could be cut some way to make it less than 2" but that would be a real PIA.