We cannot say for certain which between Simmons, Sealy and Serta is the better mattress. I cannot speak for you on what can bring you more comfort when you are sleeping. In fact, it is difficult to find a mattress that provides all the things we need.
However, to answer the question "which is a better choice", I would have to say Sealy. Mind that I have only arrived to this conclusion due to the lesser complaints thrown at this company and the higher satisfaction rating they have received. When one is comparing, one should look at the bigger picture.
Leather Futon Sofa
There really is not that much of a difference. Only that, each have a specific attribute that they excel on. For instance, Simmons offers better spring beds with their beautyrest line. Sealy offers better memory foam and latex technology with their posturepedic line. Serta is just in between.
What you might want to consider is what mattress can provide you with the comfort you are looking for. If you cannot personally test the bed or sleep on top of it for a few minutes, read reviews. This would be a bigger risk since you are not personally testing the mattress out, only taking into consideration the opinions of other people who have closely the same preferences as you are. Remind yourself that comfort is relative.
As for the other essential mattress pointers, Sealy is leading the race. For one thing, there is almost a unanimous agreement that this company has the best customer service. We all know how difficult it is to complain about your purchase once you have already sealed it. It is easier to buy something than return it when it proves to be a useless pile of foams.
According to some people, Serta has the worst customer service saying that their representatives will have to ask how severe the damage is to the mattress. If the bed is not damaged enough to their estimation, you will have to pay for some service charge to get someone to fix it for you. Also, the return delivery charge falls on the shoulder of the consumer. If you happen to have bought a heavy beds, you will have to spend more on shipping.
I am not an expert in consumer guides but I know for a fact that it is better to choose a reliable company that will not lead you to a merry chase when it comes to its warranty. This is probably why Sealy has been putting the others in the shade for quite some time now. They place the interest of their consumers first above everything else to make certain that they will come back and buy again from them. That is the whole logic of the over-all satisfaction rating. When more consumers are satisfied, more will recommend it and more will keep on coming back.
So in general, you have to test the comfort of the mattress first and get to know more about the reputation of the mattress brand before giving your plastic and have them charge you with thousands of dollars.