I like the concept of the $5 gem pack and the $50 Deathknight armor pack. I never bought any of the $5 gem packs, but I would have if it was an option when I started.
For future purchases, I like to buy things that can reduce grind time. The only purchases I have ever made in this game is enough gems to buy Dragon Armor back in December 2014 when armors had resource bonuses added to them. The other time was the recent Deathknight Armor pack.