Also, just from what I've heard from people, people who have sporting dogs don't usually like herding dogs and vise versa. There are a few people who can take both, but usually it's either one or the other.
Or maybe I'm just the oddball. Hmmm...
You also need to define what success means to you in your sport of interest. In agility, do you want to move up through the titling levels? Do you want to go for champion titles (MACH, ADCH, etc)? Do you want to be flashy and go for blue? National level? World level?
Webby is a super MACHing dog. He earned his last QQ and his last points one trial apart (vs. your fast dogs but maybe less consistent who have all their points long before their QQs **coughMiracough* or your slower dogs who almost always QQ but can't get the points) and actually places in classes fairly regularly though he is usually 3rd or 4th, not 1st or 2nd. Mira is more of an adrenalin rush who is competing for the top spot in her classes but, being both big and fast, isn't quite as consistent though she is coming together well considering her age and our rather low trialing rate. A friend's dog I sometimes run is pure adrenalin and is just breathtaking to run or watch but he is also very very difficult to run, requiring clear directions 3-4 obstacles in advance and with no room for error whatsoever...even shifing your weight inappropriately can result in a wrong course.
Everyone has a different goal an comfort zone, and none are wrong as long as you find a dog who is a good match for you. The flash is fun, but those solid meat&potatos dogs who send you home every weekend with a stack of ribbons are awfully nice.