I'm trying to grind to 100 Enchanting skill. Will enchanting an item heavier than an Iron Dagger net more experience?
No it does not.
It doesn't matter what you enchant, it only matters how many things you enchant, and the level of the enchantment (dictated by the size of the soul used).
The fastest way to level enchanting is to get as many iron daggers as you can, and enchant them with your most expensive enchantment with petty souls (or higher if you run out, but use the lowest level ones possible).
As a side effect you'll also make a lot of money selling the daggers.
To answer your question, it really doesn't matter what item you enchant and it doesn't matter what kind of soul gem you use to do it, you still get the same amount of progress towards leveling your enchanting skill. I really recommend getting gold ingots and smithing as many gold rings as you can, they will be plentiful since you get 2 per ingot. As an added bonus they will sell for quite a lot more than the Iron Daggers.