You can’t go wrong with either shelter IMHO. As a tarp-only, I’d pick the Deschutes. As a tarp plus inner tent combo, the Notch may win out depending on your needs. Both have similar 30d silnylon fabric tarps, so the differences boil down to features.
Both shelters have the versatility to use the fly-only when the weather’s nice, which you may appreciate in California in July and August. However, the Deschutes is probably more taylored as a standalone tarp than the Notch Fly. That being said, the Notch fly (tarp) is very roomy and you can use either door, depending on wind direction, which is a nice benefit provided by the Notch.
As for inner tent, the Notch’s inner is wider in the center and narrower at the head and foot. In contrast, the Serenity inner net for the Deschutes has a more “normal” rectangular floor that may fit wide pads easier. Also, the Notch gives you a little more head and toe room while sleeping than the Deschutes does. However, the two Deschutes side panel tie outs can be used to greatly increase room above your head and feet, at the cost of two additional stakes.
Another difference between the inners of these two shelters is that the front door panel on the Serenity inner is vertical, whereas the Notch’s inner is angled slightly. What that means is that if it’s raining gently with no wind and the tarp’s doors are wide open, the the Serenity net tent under the Deschutes will remain dry. In contrast, when the Notch’s doors are open all the way in light rain, you can get a little moisture hitting the bottom corners of the Notch’s inner net tent (at least on TarpTent’s 2015 version of the Notch). This minor issue with the Notch can be mitigated by not zipping the door all the way closed (stop about 12 inches or so from the top) – although this can stress the zipper and it’s not meant to operate in this way.
Another benefit of the Notch is the availability of a partially-solid inner net tent. The combination of the Notch’s tarp or fly by itself plus the Notch with partial-solid inner provides quite a bit of versatility for different weather conditions. You can also achieve the same versatility with the Deschutes tarp by making your own (or having somebody make) a partial-solid inner similar to the Serenity inner. This is the route that I took, making my own inner for the Deschutes, which also saved 3.5 ounces compared to the 11 oz Serenity.