We have been to both (although Playa Mia was years ago and the stay was brief due to foul weather).
We have been going to Paradise Beach since it opened.
Lounge Chairs, tables, umbrellas, clean restrooms and internet at the bar are all FREE. All they ask is that you eat/drink while you are there.
They also offer an optional wristband for $10 for all day usage of the non-motorized water and land toys. These include 2 water trampolines, 1 iceberg, kayaks, snorkeling, floats (individual and multi people). Land toys are a bungie trampoline and climbing coconut trees. Life vests are also included, but you will have to place a deposit which will be fully refunded at the time you return them.
Remember that these wristbands are optional...so if you have kids who want them..ok...but if the parents do not elect to participate...they don't have to. The boys always get the wristbands, hubby and I do not.
Lockers are available for rent. The last time I was there I think they were $4.
There are also all kinds of independent vendors if you want a massage on the beach or hair braiding, parasailing and jet skis. We have never been bothered by over aggressive vendors while we were there. We were there 5 times in a 12 month period last year.
The massages are $1 a minute with a 30 minute minimum and they are wonderful. They have you laying in a large white tent right on the beach with a light fan to add an extra breeze.
Don't worry about getting a taxi back...there are more taxis than sand in Cozumel. Paradise Beach always has taxis waiting to return you to your home away from home!!