A business checking account at Bank of America, currently. I should probably have two of them, technically, since I have two LLCs now, but I haven't gotten around to that yet.

If you don't mind me asking, I'd be curious to hear what decisions you've made on cash vs accrual accounting, pass-through vs corporate taxation, and the use of guaranteed payments vs distributions.

I know a lot depends on the specifics of each situation, but haven't heard a lot of details on this from people running single-member bootstrapped SAAS LLCs before :) .