I have a flight coming up (actually in a while) from IAD-SFO leaving at 6 a.m. I figure that I should get to IAD by 4:30 (may have luggage to check since I am going onward to KIX).

I haven't used Uber yet, though I am registered. Is 4 a.m. too early to get an Uber car from Potomac to IAD (it's a Monday morning)? Should I take a taxi instead? Thanks for any help.