Since you've been riding a while and want to learn jumping I'd vote for the Hunter hack - Talk to the instructore but I'm guessing the intermediate class. Really western is all about long legs. Jumping (small jumps) and flat riding is shorter stirrup leathers and posting the trot, and direct reining, but not that different from western.
As the jumps get bigger the stirrup leathers shorten (to a point), but as long as the jumps as smaller 1'8" crossrails and then to 2 foot verticals (and assuming you are a good rider with good balance) you shouldn't have an issue.
Can you do an "audition" ride for the instructor? That way they can gauge your abilities. Too easy a class and you'll get bored, too tough can cause you to want to give up, so best to get evaluated if possible.
Dressage is for Trainers!