Showplace is decent mid grade quality. I have a personal bias against cutesy names spelled with K when they mean C or have e's on the end. The only thing that would make me grind my teeth worse is calling themselves Olde Kustome Kabintry. If your work is good, you don't need marketing silliness.

There is a whole world out there beyond just the two brands that you mention. Don't be in a hurry to get your project done until you've done more research.

I'd want to know why your KM warped personally. Did you keep the humidity controlled in your home through the use of AC in the summer and a humidifier in the winter? Did you have kitchen ventilation to remove the cooking moisture from the home? Or, at least open a window? All cabinet lines require that basic level of home care for the warranty to be in effect. What size doors were warped? Oversized doors tend to be more prone to that than those less than 24" wide and 42" tall. Do you have any pictures of what you're talking about? KM does have a lifetime warranty, and I never had any issues with them doing a warranty replacement.

I wouldn't trust anything from a company calling itself Kustom Kabinets.

Just because your builder wants you to use either of these lines doesn't mean you have to. My GC mostly deals with Merrillat, but they are mostly considered low end builder grade which I did not want. He sent me to another kitchen place he had begun working with that carried different brands and I ended up with Dynasty cabs and have been very happy. Maybe you should shop on your own for cabinets or maybe your builder can recommend other kitchen places that carry other brands. Don't settle.