I upgraded to the Red Sea Max E-260 from a 40 gallon bowfront. It was an established tank from a local reefer that was getting out of the hobby. It was in great shape for a great price and I was able to combine both systems without losing any livestock.
Here is a simplified description of the differences between Red Sea tanks are:
S series - this is an all in one system. Where Red Sea includes all the equipment you need to get started including lights, return pump, and protein skimmer. These are their high end tanks.
E series - this is an all in one system with a smaller sump area in the back of the tank that has a small protein skimmer and power heads. These systems also have an optional sump that you can purchase. Then you need to purchase a return pump and larger skimmer.
Reefer series - this is their main tank series and it typically includes just the tank and stand. You need to purchase the equipment for this like return pump, protein skimmer and power heads. You have the flexibility to set up thr system the way you want.