That was a *really* loaded question.
Do you want to make Windows programs? MASM32
Do you want to make DOS, Windows, Linux, or system-level programs, or a bootloader/OS? NASM + TextPad (Harder to implement Win32 API)
Pfft, masm is lame. Nasm 4 lyfe. Masm is for newbs who don't know native x86 assembly, and are only smart enough to use the lame macros in it, like "IF/THEN". If you're gonna code in asm, why the hell would you want to use masm? It sux y0.
Warrior, stop using MASM. If you don't, best watch yo back nigga. I'ma roll 6 deep on yo hood, and yo whole family if you don't use nasm or fasm. After them hollow points burst through yo chest, I watch with satisfaction as you bust into a spasm. That's another reason you don't use masm, children. I got an AK-47 with magnum armor piercing shells, yo.
Stop feeding The Man, he only wants you to use MASM32.