If the LLC (or any other business entity) - regardless of its location - has an employee in CA - that means - the LLC is doing business in CA - and according to CA law - should be registered in that state, collect and remit employment taxes, registered with CA Department of Industrial Relations - collect and remit FUTA taxes, etc.
If the LLC do not do these - it will violate CA laws.
In my mind, that would mean I am an employee of a Delaware, LLC with SCorp elections, who is residing and collecting a salary while in CA. So, would I not register the LLC in CA, but keep it in Delaware and pay taxes on the income that I get paid on the W-2?
If your workplace is in Delaware - same is true for Delaware registration - and the Delaware LLC would be required to pay Delaware taxes - because it would do business in that state - and you would have income from Delaware sources and therefore would be required to file non-resident Delaware income tax return and will owe some taxes.
Before moving forward - you need to determine - regardless of registration - where the LLC is doing business - having employees in a specific state - means doing business in that state.
S-corporation vs C-corporation:
C-corporation is taxable entity and pay its own income taxes - in some circumstances it is beneficial, but if any dividends distributed to shareholders by C-corporation are subject of double taxation - on corporate and on individual level - so if you plan to distribute income to yourself - there will not be any benefits from tax prospective...
However if you want to keep money in the corporation, purchase some business properties - you may have some tax savings.