Generally speaking, topping is more predictable than FIMing unless you're really experienced with it, and are able to pinch/cut the growing tip at precisely the right spot, otherwise even if the cut/pinch you make is only very slightly above/below where you did the time before, the results you get will vary sometimes even to the extent of the plant not even looking like it's been topped when you don't pinch low enough. This is the only reason that I prefer topping, because you know exactly what the impact will be. If you have the time to experiment, I'm sure it's worth trying out FIMing for yourself. But if you're in a situation where, like with ScROG setups, that you NEED a certian amount of tops, I'd do regular topping once or twice.