I generally try to make strong splits. That is at least a ten frame deep's worth of bees, brood and honey (two eight frame mediums worth) which means the hive has to have TWO deeps' worth of bees, brood and honey before I split them (four eight frame mediums). That way they have the critical mass to take off and not struggle for a month or two before they take off...
It also depends on having drawn comb. A split can really take off with drawn comb rather than bare foundation or empty frames.