For my Warrior, who often plays a Swordsman, I will choose a blade with 15^50 or +15% (while in stance), depending on the situation. If I am going to be using stances near constantly, then I will take the +15% (while in stance) blade. If I am going to be doing more of a spike concept, then I will go for the 15^50. Even running an Adrenaline based build, it's always nice to have the max energy you can get for that special energy-reliant skill in your bar.
My Ranger, on the other hand, is quite fond of +15% damage, -5 energy bows. I wear Druid's Armor, so while weilding my -5 energy bow, I have a total of 27 energy. This is more than enough for my Archery build to work with; I rarely, if ever, run into energy problems. Though I will say that I weapon-swap with the green vampiric Ironwing Longbow; so my max energy fluctuates between 27 and 32 quite often.
In the end, it's all a matter of personal preference, and build design.