I used to go to Pasadena weekly for work and always flew into LAX for a couple reasons. First there were direct flights so it saved me time connecting. Second, there were more options for IROPS. And finally, the price was almost always better flying to LAX.

That said, flying into BUR will significantly reduce your driving time to Pasadena. LAX to Pasadena can be brutal depending on what time of day you are going. I would always fly out on Sunday nights to avoid the traffic but returns on Thursday evenings were awful. If you are getting in around rush hour on Thursday your drive to Pasadena will not be pretty. Sunday coming back shouldn't be terrible but you never know in LA.