I live in Washington state and I have a fulltime w2 salaried job with full benefits (health, retirement, etc.) and say I make about 150K in salary+bonus. I am starting a second job as a hourly contractor where I am expecting to make say about another 150K if I go for corp-to-corp or 140K if I go w2. Both jobs are WFH/telecommute. What would be the most beneficial / tax saving option for me to start the second job as? I was thinking of going for corp-to-corp and opening a single member LLC with S Corp tax election. Any advice? THANKS!

Since you have benefits coverage under the first job, I would be more inclined to take the second job as a contractor. There are some advantages, primarily in liability issues, to an LLC vs a sole proprietorship. But with your income, you can afford to hire a CPA to advise you.