There is very little to no benefit these days in using 32bit installs where 64bit ones are supported. In fact, the most recent CentOS release has dropped support for 32bit all together. Unless you have some very specific reason to choose 32bit, 64bit is definitely recommended even on lower end systems. The main reason to continue to offer 32bit options at this point is to provide support for some proprietary legacy applications which don’t offer 64bit versions. Even this has become less important with multi-arch support on newer Ubuntu releases which allows you to natively install 32bt libraries on a 64bit machine.