We've not seen the exact fare rules yet. Basic Economy may only be available for purchase 14+ days out. If that's the case, I won't even see the option for my business travel.
My corporate policy is "lowest logical fare". I latch on to that middle word with great relish. My practical policy, when its not internal (that is, when it will be passed onto a customer) is "what I'd do with my own money", which usually is low-flex.