Ricki - I assume you’re talking about kitchen countertops. I’d go for 3cm for countertops. We replaced 3cm granite with quartz. If we’d used 2cm a plywood base would have been needed to raise the countertops so we didn’t wind up with lower tops than the granite. We weren’t replacing cabs. For the 2cm an edge has to be made & attached to give it the depth. That’s a seam. We didn’t want that. My understanding of uses for 2 & 3 thickness is the same as yours. You can confirm or disapprove what designer is telling you by walking into a tile / stone store & just ask which is generally preferred. As for the Home Depot prices - they’re getting a huge volume discount on patterns provided exclusively to them. You cannot buy a pattern they have from an independent stone yard or another dealer who sells that specific brand. I tried with the Cambria brand quartz I wanted. Home Depot carried it & I couldn’t buy it from them & have my own chosen fabricator cut & install it. Home Depot explained their pricing includes all the fabrication & install & they can’t break up the cost. It’s also a contractual deal between them & their suppliers.

ETA - remind your designer who the customer is…..

"She is also quoting us 30% more for slabs+fabrication than Home Depot."

No one can touch the big boxes for prices. It can't be done consistently. Their volume leverage is overwhelming and they have the largest and most efficient fabricators under contract.

Thanks - realize my inquiry wasn’t quite clear but you understood me anyway.
We are already familiar with how Home Depot works; we’ve been out to see the inventory at their slab distributor, and talked to their fabricator. As happens, our project went from replacing one or two cabinets to replacing all of them, and we are much more cost aware now. But we will be using the kitchen all the time, so we are still going for what we want. Within reason.

2 cm vs 3 cm is very region dependent. I remodeled a kitchen in CA and majority of slabs sold were 2 cm. I used 2 cm Taj Mahal with a laminated built-up edge on a plywood base. It looked fine. Mitered edges are also an option.

A few years later I built a house in FL and majority of the slabs sold are 3 cm. This time used 3 cm Taj Mahal and all that was needed was an eased edge. It looks fine too.

The prices for both projects were comparable, when you take out the covid component of the new build.

If I had a choice I would go with 3 cm, because it is a simpler edge and you eliminate any issues with a glued on laminated edge or mitered edge.

Thanks. We are going with 3 cm. Now on to the next decision!