it really depends on your strain man, some strains will produce more bud if topped, and because of genetic cloning and selection others might produce less.
topping will produce 2 top collars, and you can top these too but this requires a bit of experiance.

the best thing to do is say if you have 10 plants is to top 5 of them and then see which ones produce more bud. a bif of experimentaion will help you if you stick to this starin in the long run.

i have found that pure indicas or mostly indicas do not require topping,( as they generally produce a fat top collar) but a few sativas in the past have produced more bud after being topped compared to those that have not.

also depends on the amount of light available but this is another story.

hope this helps

psy