For general strength, I'd recommend higher reps (12-15) with shorter rest intervals. Using time rather than reps can also be a nice alternative (i.e. 30' on / off). For core development, I think you could use all types of rep / set / rest interval schemes ranging from the one recommended for general strength, to timed static holds, to high intensity, low rep, long rest interval options. This would just depend on what specifically you're trying to accomplish with the training.