If I want to pursue a career within special operations in the Army or Navy, which branch offers the best opportunities?

With the Army, you begin your training path with Infantry OSUT (one station unit training), which is basic training and then Infantry training. Followed by Airborne School. If you have a Ranger contract or 18 X (Special Forces), you then enter their respective training pipelines. If you wash out of either of those, you are already a qualified Airborne Infantryman and will be assigned as such. With the Navy, if you washout of any step of the SEAL training pipeline, expect to be reassigned to the "needs of the Navy" and likely spend the rest of your contract as a sailor aboard a ship. Not necessarily a bad thing if that is your cup of tea, but you won't be jumping out of planes in a ground combat arms job.

Everyone wants to be "SPEC OPS"
Do you know what you actually want to do? You should consider what type of work you like when you're one of the 95% of people who join the military planning on going to some type of special operations and washing out. That percentage is probably an exaggeration... It's probably higher. My RIP class had 200 people show up. 90 people start. 30 finish. That doesn't even count the multitude either failed Airborne school or quit after.
My point is, you should think about a different job and join as that. When you've trained a while, then try out for a selection. Otherwise, you're going to come in on a special operations contract, most likely fail, and be reclassed to whatever the service you're in needs.

Have you taken the ASVAB yet? What are your top three skills? Do you live close to a base that has the jobs you are looking for? What are your grades? Are you athletic? How much time do you spend outdoors in a day? Do you have a serious girlfriend? What are the top three reasons you want to join Special Forces? Suggest taking the leap one step at a time. First recruit training, then advanced selection.