Assembly language is still taught for specific platforms like ARM and x86/64. You can do a lot of interesting close-to-hardware operations with assembly for embedded code, but most high level code bases like business logic code don't really use it directly. An assembler is generally always involved for higher level coding languages that compile down to machine code (e.g. C++/C, Go), because a compiler generally converts high level code to machine specific assembly before an assembler converts it to the final machine code. Something that says "ADD(Register_6, Register_13)" is much better to a human than say some fictitious machine code binary of "011010010111011101100000011000001101".
C is pretty much a macro language for assembly.
Assembly languages are low-level programming languages where you are giving instructiins like
"load from memory location 123" "load from memory location 124" "add those together" "store the result at memory location 124" "compare to memory 77" "if that location equals 4, jump to instruction 60"
Different processors have different assembly languages, so you can't run the same assembly programs on, say, x86 and ARM machines.
But which assembly to choose?
Whatever processor you're writing for? Different architectures use different instruction sets
Let’s say I want one for an amd rizen 3200. Should I pick masm? Gas? Nasm? Yasm?
They’re all x86_64 assemblers. There isn’t “assembly language” so much as a whole family of assembly languages. It’s not like saying it’s programmed in C is all I’m saying.
For x86 there are two main dialects of assembly: AT&T and Intel. Personally I prefer Intel, I think it looks cleaner with less sigils, and putting the destination operator first makes more sense with instructions like sub and especially with comparison and jump. sub eax 4 computes eax-4 and stores the result in eax, on AT&T syntax this is written sub $4 %eax so you have to read "subtract 4 from eax". And cmp 4 eax; jl label is simply "jump if 4 < eax" on Intel syntax, but in AT&T syntax the comparison is swapped to cmp %eax $4, but jl still means "jump if 4 < eax". It's very easy to get confused.
Beyond this, the assemblers are mostly different in whether they support macros and what kind. So the choice isn't too important.