(a) I’d just drive (I’ve done this quite a few times).
(b) If I weren’t going to drive, I’d take the 6:00 PM flight with 7:00 arrival, because that way, if UA were running late, I’d have three options: wait for the 6 PM flight; switch to the 8 PM flight; or give up and drive. (Of course, if weather conditions are bad enough to cancel / substantially delay both evening flights, it’s probably not a great idea to drive either).