Originally Posted by mariuszs
If you have 4GB or less install 32bit. With 64bit you have two times memory less for apps.
Since F11 the default kernel for 32bit is PAE (if the CPU supports it and nearly all do). So the decision has absolutely nothing to do with the amount of memory in your system.
64bit do not use twice the memory. Mem pointers are 64bit, and "natural" data sized are 64 bit for example, but if you declare an array of int32_t's they are still 32bit. Over many libraries the 64bit bloat factor in the memory image is about 1.5X, but the increase can range from almost zero to about 1.75X.
64bit code is remarkable faster (sometimes more than 2X) on some compute intensive apps. If you'll use cinelerra or vid processing or reduce experimental data with R you definitely want 64bit. If you are just using the system for email, web-browser etc there is no significant advantage to 64bit.