Are all human souls equal, and also better than any animal souls?

There are several soul categories for enchanting in Skyrim:

• Petty
• Lesser
• Common
• Greater
• Grand

Standing aside these, there is a category for sentient beings, Black souls. I have two questions regarding these:

• Are all black souls equal in strength? Does it matter if I use Master Necromancer's soul, or soul of some puny raider?
• Are they all greater than any of the non-sentient being's souls? For example, better even than Ice Troll's soul - which is toughest monster I met so far.

Knowing this would help me a lot in planning the enchanting.

Solution 1:

All black souls are considered Grand, and of the same quality.

The tradeoff is that black souls can only be held in a black soul gem, or The Black Star. In my experience, these are rarer on loot tables or NPC inventories than Grand soul gems, filled or unfilled.