@Sunshine-boy
My estimation is that #1 would be more secure (generally speaking) because Google use a lot of process mitigation policies with their sandbox container and all of those combined should in theory make it more difficult for an attacker to compromise the browser process for local native code execution on the host environment via RCE. When you add on features like Site Isolation, it gets even better because features like that will be beneficial against Spectre exploitation attacks taking place on the web (Spectre requires code execution within the target process, and since JavaScript is loaded by the browser process and given the features JavaScript supports, it can be done via JavaScript... however Site Isolation causes a new process per tab with the sandbox container enabled).
Even if you're using Sandboxie, let's say that Spectre exploitation was deployed through JavaScript, but you couldn't use the Site Isolation feature DESIGNED to help prevent such attacks because Sandboxie breaks the Chrome sandbox container. Despite running in the sandbox, there should still be data to be exposed by Spectre back to the attackers regarding the browser session for other tabs you currently have (or did have previously during the session) in the memory of the Chrome processes to be ex-filtrated. If Sandboxie doesn't break the Site Isolation feature, then you can ignore this part.
The reason I think #1 with the process policies is better than #2 is because it will be theoretically easier to compromise Google Chrome (e.g. web-based exploitation) without the sandbox container enabled, and as far as I know, it isn't compatible with Sandboxie which means you'd have to miss out on those Google Chrome additional security features.
If an attacker is capable of exploiting Google Chrome for native code execution on the host environment, they should in theory be skilled enough to bypass at-least some of the Sandboxie restrictions. Sandboxie injects a module into the "sandboxed" process and then patches the memory of a ridiculous amount of routines from the Win32 and Native API subsystems (e.g. KERNELBASE, NTDLL) however it also has a kernel-mode device driver for filtering process (handle creation and duplication as well as for threads), registry and file-system operations. There's a lot they will have to rely on user-mode hooks for though which they won't be able to filter from kernel-mode via callbacks... And I recon that generally speaking, someone clever enough to exploit Google Chrome for native code execution on the host environment will be familiar with API hooking techniques and how to surpass them.
I think a better alternate would be Comodo Sandbox, which utilises Intel VT-x/AMD SVM for virtualization with the hyper-visor. This type of isolation is hardware assisted via virtualization technology embedded into the CPU (e.g. Intel VT-x, AMD SVM). It's a lot more secure than kernel-mode callbacks, user-mode patching and user account isolation (which from my previous findings, Sandboxie
seemed to rely on).
Personally, I'd go for #1 based on your given choices.