First, congrads to you on the new kitchen in progress. To respond to your query (and I hope someone out there can truly help), I'm not an expert but since my family had a tile,marble&terrazzo business I do know how sensitive this an many gorgeous counter tops can be. Even with sealing them, the marble will still stain over time (esp. if used as a countertop). There are several websites that can offer assistance as a guide. Here's a link to the first site I pulled up to help give you a few comparisons:
http://www.kitchendesignsremodeling.com/compare-counterthttp://forums.findstone.com/printer_friendly_posts.asp?TID=2491ops.html
or for some additional insight here's another:http://forums.findstone.com/printer_friendly_posts.asp?TID=2491
Its all a personal choice. Quartz is beautiful, but it comes with its demons as with any natural stone does. Though the family business was closed after the 3rd generation retired, I'm thinking that the epoxy sealers out there that are claimed to make siliastone/cesarstone more stain resistant are better than what my family was using 30 years ago. I'd make the sales person prove it by applying a torch and a hot oily pan & or just hot oil to the demo tile. If you're going to shell out thousands of dollars, surely they can handle a demo like this. Sellers with demo kitchen stations may be more willing to do this than others. Time to do some research for sure and good luck.