If you had to choose between 2" and 2.5" thick concrete countertops, which would you opt for and why? Side note: I've heard that if you go bigger than 2" you need to start adding rebar, etc
More important than the thickness is where you place the reinforcement. Concrete handles compression well, but breaks easily if stretched. A section that overhangs the support will be stretched on the top surface and compressed on the bottom, so the only reinforcement that will help there is close to the top surface. If it is between supports so it will want to sag in the middle, the most stretching will be on the bottom, so that's where reinforcement needs to be. This would be in addition to measures like fiber for general strength.– fixer1234May 10, 2017 at 19:58
I'm going to call this an aesthetic choice. But a bit of remesh/rebar wouldn't hurt, especially in a 60" long chunk or around a sink opening.
Personally, I'd find 2-1/2" overly heavy.
If you use fibreglass mesh (on a roll), you can make the thickness 40mm, which would be much lighter, & easier to handle.