i use 64 bit program if its available in x64 version since its process faster.
e.g. WinRAR x64, Adobe Softwares, Firefox (Nightly x64), Thunderbird (EarlyBird x64), MPC-HC, etc
i will use 32 bit if there is no x64 version of software and have known issue of problem.
e.g. Microsoft Office 2010...