BackTrack 4

the highest rated and acclaimed Linux security distribution to date. BackTrack is a Linux-based penetration testing arsenal that aids security professionals in the ability to perform assessments in a purely native environment dedicated to hacking. Regardless if you’re making BackTrack your primary operating system, booting from a LiveDVD, or using your favorite thumbdrive, BackTrack has been customized down to every package, kernel configuration, script and patch solely for the purpose of the penetration tester.

it contains about 300 pre installed tools :)
official change log for bt4 r2

• Kernel 2.6.35.8 – *Much* improved mac80211 stack.
• USB 3.0 support.
• New wireless cards supported.
• All wireless Injection patches applied, maximum support for wireless attacks.
• Even *faster* desktop environment.
• Revamped Fluxbox environment for the KDE challenged.
• Metasploit rebuilt from scratch, MySQL db_drivers working out of the box.
• Updated old packages, added new ones, and removed obsolete ones.
• New BackTrack Wiki with better documentation and support.
• Our most professional, tested and streamlined release ever.

 yes i would totally recommend you guys to use backtrack instead of other distros reason:
Backtrack is owned by offensive security they guys update it regularly+it has biggest community support in terms of hacking distros.

problem with backi was lack of hardware support.

you can download BACKTRACK from here(vmware&iso)