If you're really interested in competing, I'd suggest going with the BJJ. HKD doesn't really have a competition scene in the US (I'm assuming the NJ in your name is for New Jersey), and doesn't tend to be very sport-focused.
As for what HKD has to offer... first off, I should say, HKD is very decentralized, so every school is going to be different.
That being said, Hapkido is hybrid art, combining standing grappling with striking. Some schools also include some basic ground grappling to be more comprehensive, but don't expect a lot of detail on that like you'd get in BJJ. HKD tends to avoid going to the ground, taking a general approach that could be summed up as "throw the bad guy on the ground, kick him in the head, and escape".
In my experience, Hapkido tends to have more focus on small joint manipulation compared with BJJ (lots of wrist locks, fewer leg locks or chokes), and more shoulder throws and sweeps. I personally like that, because the self-defense situation I'm probably most likely to encounter is "sleazy guy tries to grope me", and IMO a standing wrist or arm lock is a better solution to that compared with a triangle choke (less likely to get me in trouble anyway, lol).
How much of a workout the class provides is going to entirely depend on the school. It could be anywhere from easy to intense.
Ultimately, I think you need to just go and take a class and see how you like it.