If your labels do say "high, medium, low" and this not just an example, then I'd say the first version is better, because it also illustrates (in a way) that the first one is "higher" than the others (and also, "medium" is in the middle, "low" is at the lowest position. On the other hand, if you had labels like "left, middle, center", I'd choose the second option.
Generally speaking, I think that it depends on the actual content. If the labels are not suitable for this kind of illustrating, the best way is to be consistent with the rest of the UI.