They are my favorite because they get the most light but I run scrogs and have 100's of top colas...so IMO they are the best but it doesn't really matter as long as the buds are getting equal light...
Sometimes the top bud gets the most light and has less taste and smell as a result. I think there is wisdom in not having the light too close to the tops of the plants, or in the case of a SOG/SCROG. Using LEDs I grew smaller plants with smaller buds that were fully developed all the way to the bottom of the plant and the dankest Afghan Kush I had ever smoked. I find some buds have better tasting smoke from the bottom of the buds than the top.
For the most part top to bottom, the potency will remain the same. If my lower nugs did'nt get good light or are a little behind the rest I remove the tops and let the bottoms go a few days longer. Also like using bottoms to make bubble.
Yeah the tops are the most potent "best" part of the plant for "intoxication" purposes. Even at lower branches the buds are "top colas" The most THC resides in the tops of the plant. Even the roots have THC but much like warm air the potency is going to go to the top of the plants. The buds, leaves, stems, then roots maintain THC potency in that declining order. Anyone care to challenge?
PS: I use intoxication in quotes because I don't think that anyone is poisoned by natural organic Cannabis.