it's all up to you really. Just remember topping causes strees for a bout a week, as Total Head said, and LTSing causes very little stress. Just think what you want your plant to look like, and when you want it to look like that. So think about how long you plan on vegging, and then work it out in your head. I'm acctually planning on doing an LST around the bucket, and THEN topping right before it reaches all the way round. I think I may do one the same as Total Head as well, with two tops going opposite ways around the pot.