Congrats! And welcome to the forum. Have you traveled to both places? I just got back from DR and went to Aruba a couple of years ago. I'd say they are pretty different places. The DR is mainly all-inclusives and while there are plenty of things to do off of the resort, I definitely felt more safe out on my on in Aruba. I would say that the DR is more affordable and Aruba is more americanized, only a few all-inclusives with some amazing restaurants all over the island (but most are pricey). I think it really depends on what type of atmosphere you are looking for and what is affordable for your guests. Let me know if I can answer any questions for you.
Happy Planning!
Julie