This recent thread comparing Curacao to Bonaire should help you get an idea of how to plan a trip to Curacao and your options for it. A key question is what kind of diving you will do.
I did 2 dives on a cruise ship stop in Cozumel, independently booked with Living Underwater, which has 120 cf steel tanks so you can stay down a good while. Would love to do it again. Have been to Bonaire 7 times, well over 100 shore dives there, haven't set foot on a boat in Bonaire yet.
On a Cozumel trip, you will stay at a resort (e.g.: Scuba Club Cozumel) or a hotel, and dive (perhaps 2 dives/day?) with a charter boat op. - Living Underwater, Aldora, Blue Xstacy (? spelling) seem well-regarded on the forum, and there are others. You'll be doing guide-led drift dives, reef topography varies substantially across sites, and you're fairly likely to see some 'big' animals. Drift dives keep you moving along. On my 2 dives, I saw a big black grouper, a large eagle ray swam right up under us, a southern stingray was seen in the distance, a huge green moray came out behind me and I never saw it, and I saw a channel cling crab - all this over 2 dives.
Curacao diving is likened to Bonaire. Bonaire shore diving often involves a shore entry, then swimming parallel to shore along a reef that slopes at a roughly 45 degree angle, looking at hard corals, gorgonians, sea fan, etc..., lots of smaller fish, some mid.-size (e.g.: school masters, blue-striped grunts, parrotfish, spotted morays), and occasionally something bigger (barracuda, green moray, a few sea turtles (only greens & hawksbills for me so far) or tarpon.
Bonaire's appeal is diving any time of day or night you feel like, without advance planning or anybody else's schedule, no guide needed in most places, and you can dive again & again, as much as you can stand, and rack up 20+ dives in a week. Most sites have little current. You'll probably dive nitrox EAN 32 and only use 80 cf tanks (unless you prefer smaller). Since it's a longer drive between sites on Curacao, I suspect you won't be racking up as high a dive count there.
So, if you compare more diversity & bigger animals drift diving guided dives with an option for big tanks with some op.s, to a larger number of shorter shore dives with smaller stuff but done on your own schedule, what sounds more fun to you?
Richard.