1. If you book and need to cancel or switch to say, an on-time flight on another airline when yours is ridiculously delayed, you’re likely to be eligible for a full refund, either under DOT regulation or airline policy.
2. Larger airlines (United) are more likely to land longer flights on time than smaller (Virgin) during inclement weather, since they can prioritize their own airport traffic and cancel shorter, regional flights.

So, if you know you need to get somewhere for something that matters to you (in my case, taking care of one of my customers) — swapping from the cool brand you prefer to the stodgy one that delivers might be easier than you expect.