When comparing NASM vs FASM, the Slant community recommends NASM for most people. In the question“What are the best x86/x64 assemblers?” NASM is ranked 1st while FASM is ranked 3rd.
Ranked in these QuestionsQuestion Ranking
Pro Clean syntax
Pro Powerful macros
It can do everything GAS+CPP can do combined, and much more.
Pro Excellent for toy DOS code
NASM can easily create .COM executables and is even supported on DOS.
Can be used from .NET with Fasm.NET.
Pro Open source
The complete source code is included.
Download size only 1035 kilobytes for Windows, 342 kilobytes for Linux.
The Windows version also includes an integrated syntax-highlighting editor.
Con Poor diagnostics
NASM typically won't tell you the problem, just generic parser errors like "mismatched operand type" or "expected instruction".
Con Low level
Not supporting as many high-level statements as MASM or TASM.