Among Caribbean destinations, Curacao isn't especially popular for its diving. If
those were the only two choices I'd go to the Seychelles even if it meant it wasn't
going to be a serious dive trip. YMMV. Besides the diving, what is it you like in a
destination?

I haven't been to Seychelles, but have a buddy that lives in Curacao I
make it a point to visit (and all of the young topless Dutch women have
nothing to do with it). I really enjoy Curacao but I'm not sure it
would be as good a time if I didn't know someone living there. 9 days
would be a long time to stay there, I think.
   There are enough dive spots that you could easily get in the diving
you wanted, but you may have to travel. Nice island, no rain (desert
island), lots of cactus, walls within swimming distance of shore, at
least at the sea aquarium end. My buddy runs the Curacao Sea Aquarium
so the last time we went, we stayed on the landlocked boat with him and
his GF (and 4 young dutch female college students), at the entrance to
the aquarium. Walked into the aquarium everyday, threw on their gear,
jumped into the grotto they have cut there, and swam out through the
break in the rocks to the reef and wall.
   If I was going to stay somewhere I had to pay for, it would still
be that end of the island by the Sea Aquarium. Nice beaches, 5 bars
(the best on the island) within walking distance, beach diving, dive
shop/boats right there. Make sure you do the happy hour shuffel. The
bars all stagger their happy hours so when one ends, you walk to the
next one. There is a fair amount of surf because of the constant sea
breeze. Also dont let it scare you if the rooms have no air. There's no
need with the breeze and low humidity.
   As far as the rest of the island goes, you will need to rent a car.
Spend a day in Willimstead (sp?) shopping and site seeing. Take a
camera for the interesting colors and architecture. See the floating
bridge and the water market. Tour the island. You can hit most of it in
a day or two.
   Theres an interesting golf course if thats your thing. Really well
set up using the natural desert terrain to make for a great course.
Take a camera, some of the holes are spectacular. My only gripe was
that being a desert island, the greens were not very green. All of
their water is desalinated (for the whole island) so it's too expensive
to water and they get no rainfall to speak of. Oh, their rental clubs
are Calloways. Being desalinated, you can also drink the water from any
spigot or faucet on the island.
   Eat at the ostrich farm. It's a bit expensive but well worth it.
Try some of the raw ostrich dishes. Get used to Polar beer or Grolsh.
Everything else is an import (actually EVERYTHING is an import but
these are cheepest). They have casinos but I never made it to one so
can't give you a rundown.
   Ok, I lied. Theres more than enough to do for 9 days.