JIT compilers are available in 3 versions:
32-bit client compiler (-client)
32-bit server compiler (-server)
64-bit server Compiler (-d64)
To some extent, the compiler you choose to use depends on the command line option parameters given (-server, etc.).
If it is a 32-bit operating system, then you must use a 32-bit JVM. If it is a 64-bit operating system, you can choose 32-bit or 64-bit Java. There is no requirement that 64-bit operating systems must use 64-bit Java.
If the heap is less than 3 GB, 32-bit Java will be faster and consume less memory. This is because the pointer inside the JVM is only 32 bits, and the cost of operating a 32-bit pointer is less than that of a 64-bit pointer (even if you are using a 64-bit CPU). And 32-bit pointers take up less memory.