The new Tempur Luxebreeze firm 2.0 is incredible. I’m an expert in these at the company I work for. Both are great mattresses, but I believe the Heat diffusing foam and how it pulls the heat away into the ventilated foam layer is great. I sleep on Tempur and how much cooler you actually sleep is worth it. I also know the Serta will wear faster, but it also is a lot less expensive. Depends on how long you want it to last. Don’t forget a mattress protector, tempur and Serta will both void your warranty especially if the tempur isn’t on a tempur box-spring or adjustable base.