Both are nice. Bonaire is much more quiet topside than Curacao. There are some really great sites to see on Curacao topside. Under the water in my opinion the islands are equal. I have spent 6 weeks diving along the west coast of Curacao and would not hesitate to return. Great dives, rarely do you see other divers in the water. I stay away from the bigger operations, we stay at Allwest in Westpunt, for about $100 a day you truly get diving freedom, tanks, truck and a roof over your head, what more do you need? Food, well you are on your own there, but it really isn't that hard to get good food.
Bonaire is also a very nice experience. The main reason for us going to Curacao over Bonaire is the flights in and out and given our time off, we like to make the most of it. Do one this year, then other another year. Good luck.