I've owned so many different rack systems...reptile basics hatchling, juvenile and adult racks were my first. I made the mistake of keeping them on carpet which over time warps the racks and makes the tubs harder to move in and out. They were great though, came pre assembled, w tubs, heating and fast shipping - good to go!! As well as being stackable when expanding, you really can't go wrong, rich does a great job!
Animal plastics is another great company. They have a ton of options at affordable prices. The only thing is you have to wait around 2 months to receive your order, but if you pre-plan this isn't a big deal. They are easy to put together and made well. Similar to RBI design they work well to hold humidity and heat while also providing a secure feeling for the snakes. I suggest using these if you're snake room doesn't stay at the high end of 70 or 80 deg.
Moving up to freedom breeder or ARS racks - these are serious racks for serious breeders. These will last forever with minimal Maintenance. These work best in rooms with higher ambient temps because of the open design, the lower the room temp the harder it is to maintain constant temps. That being said you can always wrap the rack to help maintain a steady temp. These are also nice because you can always add or take away levels with ease.