I was installing Wine 2.0 on Ubuntu 17.10 but I was wondering if I have to install 32-bit windows program or 64-bit if I use Ubuntu 64-bit.
WINE installs both architectures. So you can make 32-bit and 64-Bit prefixes. However, 32-bit is better supported by WINE.
Thus in most cases, the 32-bit version of the windows programs have a better success rate than the 64-bit versions. That said, it does not mean that 64-bit versions won't work.