I would go for a mellower temperment, if you are not sure you can handle the stimuation a BC needs then I dont reccomend it. wolfsoul is right BCs are working dogs, but how mellow or insane the dogs are depends on the lines , there are 3.

Barbie Collies-show bred, they can still be crazy, but have a tendency to be mellower depending on how far back the show breeding goes, the farther away the workings lines the less like a BC they tend to behave. there are exeptions but this is the tendancy lol

Sport Collies-bred for dogs sports, these dogs tend to be EXTREMLY high drive, and if you dont intend to do dogsports, dont go for sport lines lol theses dogs are bred specifly to be extremly fast, and extremly focased, and some tend to loose their brains if the working lines are bred away from too much, for axample, I have a sport collie whoes dad was rather removed for the real working BCs, he mide as well be brain dead. thankfully her mom is directly off a hog farm, and has plenty of brains lol

Border Collies-the real working bred dogs, some are crazy, which is where the sport lines came from, but a well bred working BC should have the ability to go all day and relax when asked, they require both physical and mental stimulation, and lots of it, dont provide it and they will make their own lol