This is like asking "which is better: a truck or a car?" It depends on what you need. But let's break it down so you can pick the right one, based on my own experience with both.
First, carbon steel is the pro favorite-and for good reason. It's tough as nails-can handle tapping bricks, scraping mortar, even accidental drops on concrete. My carbon steel trowel has been banged around job sites, and it still holds its edge. It also flexes just right when you spread mortar-you can get a smooth, even bed joint without fighting the blade. The only downside? It rusts if you don't clean it. But that's easy-wipe it down with a dry cloth after use, and oil it once a month. I use mineral oil, and it's never had a rust spot since I started.
Stainless steel is better for beginners or people who hate cleaning. It doesn't rust-leave it in a damp toolbox overnight, and it's fine. That's a huge plus if you're forgetful (guilty!). But it's stiffer than carbon steel-so it's harder to get that "glide" when spreading mortar. I had a stainless steel trowel once, and it took me twice as long to lay a row of bricks because the blade didn't flex. It also bends easier-dropped it on a rock once, and now it has a kink in the blade.
So, who should pick which? If you plan on doing a lot of masonry (more than a few small projects), go carbon steel. It's more work to maintain, but it'll last longer and make the job easier. If you're a beginner, or just doing a one-time project (like a garden planter), stainless steel is okay. It's low-maintenance, and you won't stress about rust.
My uncle sums it up: "Carbon steel is for people who love the work. Stainless steel is for people who just need to get the job done."
