Question # 3:

Answer:
x86-64

For me, the best assembler is the x86-64 becausethe x86-64 is a 64-bit superset of the x86 instruction set architecture. Because the x86-64 instruction set is a superset of the x86 instruction set, all instructions in the x86 instruction set can be executed bycentral processing unit (CPUs) that implement the x86-64 instruction set; therefore these CPUs can natively run programs that run on x86 processors from Intel, Advanced Micro Device (AMD), and other vendors.
x86-64 was designed by AMD, who have since renamed it AMD64. It has been cloned by Intel under the name Intel 64 (formerly known as EM64T and other names). This leads to the common use of the names x86-64 or x64 as more vendor-neutral terms to collectively refer to the two nearly identical implementations.
x86-64 should not be confused with the Intel Itanium architecture, also known as IA-64, which is not compatible on the native instruction set level with the x86 or x86-64 architecture.

http://en.wikipedia.org/wiki/X86-64