There is two types of persons here: one looking for prime, and second looking for credits, badges , and so on.

I've given up on credits almost entirely. I crunch for credits until I get 25,000 then I crunch for hours. I've reached that milestone on nearly all my active projects. Badges will happen along the way. Finding a prime is a delicious bonus.

I'm a third variation!

I initially crunched to reach a personal target 1M in the project. Then on reaching that it was to get 10M per sub-project - this is still a work in progress and is taking a very long time. To assist the process I have purchased several Xeon class server CPUs (such a shame the SuperMicro motherboards are so expensive when the CPUs are reasonably priced).

My preference is for shorter running tasks as I prefer to run my computers at idle speeds overnight so I can sleep. If a challenge is on however, I'll run my farm flat out 24/7 as I'm super competitive :)

I totally agree with Steve Hawker's observation that "finding a prime is a delicious bonus".