Both. I'll start by sweating some garlic and onions, then my garden tomatoes run through a mill, and then a can of paste, and a can of San Marzanos. I've tried that as my base. I usually have so much that I'll divide it up and freeze most of it. Then I'll take a portion of the base and add spices to it. If I think it is still too watery, I'm hitting it with more paste. If I think the tomato flavor is lacking, I'm hitting it with more SM's. Whether I'm using the fresh base, or one of the forzen portions, it doesn't matter. I can never quite hit on something that rivals the jarred sauce my wife and I like, or rivals what I've had at restaurants.
The one thing I do like is some fresh canned SMs warmed up with some fresh basil strips tossed in, and served over good ravioli. I had that at a restaurant once, and I've done it at home. Other than that I've got nothing.