I use both. I use them interchangeably. I don't notice any real difference, however, I usually don't have the same variety in both pellet and leaf at the same time.
Leaf is more effort:
- They take up more room in the freezer
- They absorb more wort in the kettle
- They need to be bagged and weighed down when used for dry hopping
- They absorb more beer when used for dry hopping.
If you use the hops wet (fresh), use within a few days off harvest, and as noted by 'ong', use about 5X weight in the recipe, and use a known hop for the bittering charge.
If you can get about 1.5+ lbs of wet hops, use them all in a Pale Ale. Don't mix them with any other flavor hop. That way you will find out what they are like, and if worth using again ..... maybe even figure out what they are.