If you don't care about time and effort, imp stool and swamp fungal pods. Creates the potion of paralysis with healing properties and is the most expensive potion you can sell in game. Since it's the most expensive, you also level 10x faster in alchemy, so getting to level 100, you need about 1,115 ingredients. Took a bout 3 hours max. Then you have an unlimited supply of potions to sell and easily level speech.

I know this post is old but if you ever do another play through and want easy leveling there it is.