Yeah, they are optional mega-bosses after all. (The 'white weapon' is 'Diamond WEAPON'.)

Personally, I believe Ruby Weapon is harder. You generally fight it alone, and it has an abnormally high body defence. Weapons won't cut it unless you max your stats, which would help anyway. Generally I see people using 4x Cut, and Many sets of Counter Mime to waste him. There's also casting Hades or using Dazers to stun him (Hades lasts a little bit longer), and Miming KOR W-Summons until it dies, with Final Attack/Revive to revive you. That's what I did when I beat them the first time. W-Iteming two Hero Drinks (or more) to increase stats to the max also helps. (I see alot of that, at the least.) What I did, was just use W-Summon, once on the tentacles, and once on the body. Then when the claws go back, when you mime it, the main body gets two KORs in his face. He will counter with an Ultima, but you should be wearing a Mystile anyway.

As for Emmy, KOR is another common (tedious) way of killing them. Another popular way is to use 8 Counter Mimes and waste it in one turn with Cloud, Cid, or Barret with 8 Full Omnislashes, Highwinds, or Angermaxes. (As you can see in the infamous Yarikomi video.)

Either way you do it, it requires a little bit of time with the Magic Pots to level up that Materia, since it usually requires pretty high-leveled advanced Materia. There are those that use other strategies, however....