i386 or x86_64 for my new Dell laptop
 

I plan to install Fedora on my laptop.
But I just confuse which one is right for me.

My laptop is

Dell Latitude E6420 (ODM CTO)
Intel(R) Core(TM) i7-2620M (2.7GHz, 4M cache) with Turbo Boost Technology

With 6 GB Ram

Please advise.

With i7 processor, you should go with 64 bit version to take the full capabilities of it. Though with i3 I am running 32 bit on this laptop :D
If you have 4gig of ram or more you need 64 bit version to use the complete ram.

I would also go with 64 bit on that machine.
Just one side note: You do not need a 64 bit OS to address more than 4GB RAM (although I would recommend it).

The prior posts are good advice. It may help more to know what you expect to do with this laptop.
For normal laptop user I may agree that either is fine but I'd almost be in slight favor of the 32 bit, but I'd most likely put the 64 bit in unless it gave me issues.

My suggestion:

If you're worried about memory usage, go with 32-bit (32-bit applications tend to use less memory than 64-bit applications). If you want to take advantage of the various extra features of the CPU (extended/extra registers, instruction set extensions, etc.), and you don't care so much about memory usage, I would go 64-bit.

EDIT: 6 GiB is more than enough for a typical desktop user. As TobiSGD said above, it's easier to go 64-bit if you want to be able to address the full 6 GiB, but you can use it with a 32-bit kernel, as long as it's PAE-enabled.

As previously stated, it really depends on what you want to do with your machine. :-\

Go for 64x! Are you sure about Fedora as distro choice? Unless you don't mind installing non-free software manually: Flash, wireless drivers, video codecs and so on.. Although, seeing as you have a new-ish laptop it is probably best to have "cutting edge" type distro running new kernel versions.