Focus Blast can be a mixed bag for me. While at times, it is very useful. 120 base power is nothing to sneeze at. And it allows most Psychic-types to bypass the problems they have with Dark-types, since Signal Beam is another option, but much more limited in how its distributed. I like Focus Blast, as it does seem like a more common variation on Aura Sphere, but the 70% accuracy is a bit shaky at time, even with something like a Wide Lens or Zoom Lens.
I feel the lower accuracy is to balance it out due to its higher power (after all, so far, the only moves that have 100 base power or higher with no drawbacks are Earthquake and Judgement, not including a full-powered Magnitude). Sometimes, though, that 70% accuracy seems too unreliable, so it prevents it from being a massive staple in most movepools. But, if one is lucky enough, then it can be a brutal attack, especially since, as a Fighting-type move, it can smack five different types with major damage. And for special hitters like Alakazam, Gardevoir, and Infernape (okay, the last one is more of a mixed hitter, but you get my drift), it can be a valuable weapon, since moves like Signal Beam are more limited in distribution. So if one is willing to deal with the lower accuracy, and a bit of luck thrown in, it can be a very valuable move to deal some impressive damage.
As for the concept of Focus Blast, it seems to embody more of a fighting spirit of the Pokemon vs. what Aura Sphere is; Aura. Both are different forms of energy. While Aura Sphere is far more useful, thanks to its fairly high power, perfect accuracy, and range of effect, Focus Blast can be a substitute, as it embodies the Pokemon's will and spirit. Since most Pokemon who can learn this move are full-evolved, it only makes sense, as they've had more experience in battle, thus have gained a stronger fighting spirit as time went on. So Focus Blast seems like a good move to those who have battle long and hard to reach the level they are currently standing at. Again, a bit shaky on the accuracy (which mysteriously seems perfect when the opponent uses it), but a worthwhile move in the long run.
I vote for Giga Impact.
