I lived in Pasadena for 13 years and am a UA frequent flyer. I fly into BUR often, but only via SFO. I refuse to fly DEN-BUR on UX's CRJ-200 flights. I fly in and out of LAX the most, but am familiar with all of the routes to get to Pasadena in case of traffic. LAX has superior terminal facilities and flight options in case of irregular operations.

BUR is a great option for ease of baggage and rental cars, both are a few steps from the gate. There is no lounge or any decent food options gate side, but there is free wifi.

FYI, connecting in SFO will most likely require a change in terminals via a gate side shuttle bus.

I find ONT and LAX to be about the same driving time for the most part, if that helps.