Wetsuits come in many different thicknesses, sizes and styles, so it is important to choose wisely for the kind of diving you are doing. For the purpose of abalone diving in Northern California's costal waters, you will want a wetsuit that provides protection from this colder water. You will find divers up here wearing mostly 7 mil suits.
The most common types of suits that you will find are going to be the Farmer John, the full suit, and the full suit with an integrated hood. The "Farmer John" style is going to be a little warmer than a full-suit because you are actually having multiple layers of 7 mil covering you. While the full suit style will give you more mobility and require less weight to get neutraly buoyant at your desired working depth. However, some manufaturers are creating the full suits with various thicknesses in the suit. The full suit with the integrated hood does add warmth as you won't get those shots of cold water down the back, but they are difficult to put on, and your mobility can suffer in them.
There are a lot of brands to choose from. Here are a few that offer great quality suits: Akona, Bare, Body Glove, Camaro, Deep See, DSET, Henderson, Mares, Neosport, ONeill, Pinnacle, Tilos, XCEL, and XS Scuba
Some abalone divers will wear a dry suit, but they are few and far in between. The dry suit does offer excellent protection against the cold, but it also traps a lot of air which makes getting yourself weighted properly extremely difficult as the amount of air being trapped can vary each time you don your gear. Plus when you are at depth and the air is squeezed you can become extremely negatively buoyant and start descending way too fast for you to control. Overall the dry suit is just not a good choice for abalone diving.