I hope this doesn't come off the wrong way, but Master Hand and Crazy Hand are not Mario characters, and shouldn't be apart of a Mario Melee that is if you wanted to keep this strictly to dealing with just characters from a Mario game.

Crazy Hand and Master Hand actually belong to the Kirby series, in which they can be found in Kirby & the Amazing Mirror.

As for the fight goes, it should probably go to Mario and Luigi. The two work good together, and can defeat Booster or Fawful. As for Giga Bowser, well Mario and company has taken him on in various large sizes (larger than his normal form that is)as evident in Super Mario 64, Super Mario Sunshine, Yoshi's Island, and Mario Party 5. Still Giga Bowser looks more fierce than just a grown Bowser, but the combined team of the Mario Bros. might be able to take out this form as well. As for Master Hand and Crazy Hand, well if Kirby can do it, then I have faith that Mario and Luigi could as well. So my verdict for now will be the Mario Bros.