Welcome to the site and congrats! There is definitely no shortage of information here, and you'll find the brides, both past and present, very willing to share ideas and tips!
You present 2 very different markets in terms of destination weddings. Firstly, the site owner Tammy is a Cabo bride so she would be a good source of info. A large number of brides on the site are heading to Mexico, so again tons of info.
I would highly recommend reading the resort reviews to see what past brides have experienced. That's a good way to see what the resort could offer. Otherwise, it's research! I know you'll get recommendations from other brides but it will boil down to what you want and like. Cancun is definitely a party city, and some people will stay away from Cancun for that reason.
I would also definitely recommend a travel agent! First of all it will make life easier for you, and for your guests. As well a travel agent will be the best person to help with suggestions for resorts and also to let you know if the resort has any promos available that will benefit you and your group. you don't say if you're in the US or Canada but the site owners - Wright Travel are destination wedding specialists and award winners with a couple of the chains of resorts. They have a wealth of knowledge that I'm sure will be a benefit to you. There is a contact form to reach out to them on this site. As well, they are running a series of webinars for several different resort chains that are attended by both a TA from Wright Travel and a rep from the resort. That may be something else for you to look into. They are run on Saturdays over the next few weeks and you can sign up on the site.
Good luck and happy planning!