So I've read a lot about how enchanting and smithing is way overpowered. I've enchanted a few items but noticed the effects wear off fairly quickly. So my question is, what enchantments are the best? And, is there any way to make them last longer without constantly having to use soul gems? Any other tips would be appreciated

Get a certain Daedric artifact soul gem, use your second weapon enchant as soul trap 1 second, and the reason enchanting is OP is because it can be used to boost both alchemy and smithing, and boosted alchemy can be used to further boost smithing (for upgrading your equipment via grindstones and tables). In fact alchemy could even be used to boost enchanting which boots alchemy in an infinite loop of game breaking OPness.

TL;DR by combing the crafting skills you can pick and choose how powerul you want your equipment to be, every armor set can be used effectively on master difficulty, weapons become stupidly powerful. Up to you.