Lori is my best character, in my opinion. However you will find it is different for everyone because that is the nature of gaming. I find that using the special jumps of Jazz or Spaz is actually most of the time more risky than rewarding because the amount of time you are delayed or slowed by using that move. Lori can instead take a powerup with full ammo in the shortest amount of time, faster than Spaz sidekick or Jazz uppercut, and without moving as much either. And lately I am playing as Jazz anyway. The disadvantage of jumping not as high for Lori is also true. But her advantage is speed and range of movement when taking powerups. And the ability to kick through some walls.

My take on this is probably based on Lori being most similar to JJ1 Jazz because of her jumps and me being first a JJ1 player. The characters seem more or less balanced, ignoring the fact that Spaz is the most popular in JJ2.