I have only been on Aruba
so here is what I can tell you,
I always use the cruise company tour is a little more $$$ but is way safer than discover the island by yourself.
I use private tours only on the islands where I have been more than two times, in my case st.Thomas for example.
Aruba is a friendly place you should not have any problem but if for some reason you are not on time on the ship, well the ship don't wait, check out a few Horror stories about it,
I remember one that the Adventure (AOS) left some people on Aruba.
The way I see it if your and experienced cruiser then use private tour, if you are not, use the cruise company tours.
As for the tours
There is a Tour " SEE and SEA Aruba" you can visit the island atractions and at the end of the tour you can go on the "explorer" a mini submarine like boat beautiful views of fishes, under the water ships, coral etc. A Great tour for the Kids if you have one and a great tour for the adults, also there is a good place near the explorer " EL pelican" or something like that, where you can eat food fresh from the sea.
Also if you want to drink rum punch there is also one tour where you get in a Pirate ship travel the island and drink rum punch all your day on Aruba.
If you are on Aruba visit "Carlos and Charles" that's a great place if you are looking to party and have a Good time and is walking distance from the pier.
I hope this help