Otherwise it can be rough to get good clone sites, as many have very very little side branching, or the side branches tend to stay close to the main stem and remain pretty short. Good lighting penetration helps, but I've grown a few strains where I've had to flower them out for 1-2 weeks or veg them for an extremely long period of time to get any reasonable clone sites. I think its best to get to know a plant first before you top it, my LA Confidential cut does not like to be topped at all, it can stunt her growth completely for over a week in veg.
When it comes to flowering pure sativas indoors, I think that the best way to do it is from clone, or hit 'em with 12/12 very early in growth, as you will have 2-3 weeks (or more) where you can still cut healthy clones after the flip. I have some ECSD x Appalachia I just started, and since I am expecting those to be a stretch monster I will be flowering them after prob only 2 weeks of veg time, and will just take clones before bud production begins.