We have been on the Western a few times now so I have many favs but I don't know the ages of your kids so its difficult to know which is better for your family. I'll tell you about our favorites and you can see what is better for your family.
Costa Maya is a great beach port, we have spent a great day at
Costa Maya Beach Break its all inclusive of drinks and food (AMAZING MARGARITAS & FISH TACOS DO DIE FOR!) on a beautiful beach. They had kayaks, floaties it was $40 for adults, $20 for kids and free for kids under 6 years. GREAT DEAL and a great place. You can add on wave runners and snorkeling trips from this place too.
In Grand Cayman, I have 3 favorites -
1) The
Grand Cayman Wave Runner Stingray City & Rum Point Tour which takes you to stingray city and to Rum Point Beach, both are INCREDIBLE. This is great for families with kids that are I would say at least 7-8 years of age The wave runners are a blast and the tour is excellent!
2) WE LOVED the
Cayman Outrage Eco tour- Stingray City- Star fishing beach & Tubing it was a private tour, but worth every penny. You can customise it and decide where you want to go. Kids LOVED the stingrays and starfish!
3) then the best value for a great tour is the
Buccaneer Stingray City Catamaran it was only $39 for adults and $27 for kids and under 4 years are free!
Then for Cozumel the
Dune Buggy tour was an awesome trip and we also love the
All Inclusive Beach Break which is the best beach in Cozumel, great food, drinks, pool, water trampoline for the kids and floaties.
GOod luck with your tour choices, its never easy but there are great deals out there and a lot of fun to be had!