I'm new to Ubuntu, I have a dell Inspiron n4010 with Intel core i5 540m 2.5 ghz (1st generation), 5gb RAM. This machine have from factory Windows 7 Professional x64. My question is, which is the better Ubuntu for my PC? x64 or x32. I have read a lot of forum posts but I can't decide which is the better one for my PC.
The only reason I can think of that you would use the 32 bit version of Ubuntu in a PC with a multi-core, 64-bit processor is if you had less than 4 GB of RAM. Even then, you will still see better CPU performance with the 64 bit version, just less efficient RAM usage.
Since you have a machine that is specifically designed to run a 64-bit operating system, you should go with that. Nowadays, most applications run on 64 bit machines. Unless you have a specific application you want to compile and run for 32 bit Linux, you should go for the 64 bit version.