I'm used to see that the progress bars fill from left to right (and in some cases from right to left in rtl languages). However, in a case where you follow a step by step that will always end in a known result, it also makes sense to go bottom up; see Facebook's timeline, git's branches or what Headspace's app does.
Even though, there are still the classic numbered lists, which go top down. This seems to be the most universal way to think of steps to follow, but it doesn't look really stimulating from my point of view, at least.
For a tasklist where a task may depend on others already done, which of the alternatives gives a real sensation of progress, even stimulating the user to keep going?