Personally I find Longswords to be the easiest against it, but that's just me. It's weak to Thunder, so if you plan on using an element against it that would be the ideal type to use. It will be a lot easier to kill the Tigrex if you only attack when it's not enraged as it's pretty easy to dodge the attacks normally but when he's in Rage mode he becomes really fast. I recommend cutting his tail off if you can as it will make some of his attacks easier to avoid and can make a huge difference.
Good luck, and let me know if you have any specific problems against it!
Well, I prefer LS for Tiggy, I think either Devil Slicer or Eager Cleaver is available at that time. You could also try and thunder oriented GS . Hammers in conjunction with flash spam have worked well for me, too.
As for armor, I think at that time I had almost full Garuga (replacing the helm w/ the mask). If I recall, you an gem it for both HGE (High Grade Ear Plugs) and Reckless Abandon + 1.
If you can make it at this point, which I think you can, make Garuga armor with the mask and gem it for HGE like the other poster said. I recommend giving the fight a few tries with the proper armor and weapon before you start using flash bombs, simply because if you learn how to dodge the Tigrex properly and read its moves the flash bombs actually can become more of a problem than a help due to the fact that they cause the monster to attack randomly. I believe you combine flashbugs and bomb materials to create flash bombs, but I could be wrong since I try to avoid using them.