LOL, guess I was outvoted.
I grew up in Riverside CA where the 91 and 60 converge and I am there several times a year (was just there for 10 days and returned this week FWIW). My step-father worked in Orange County for several years in the late 1990's and carpooled daily. If we were traveling to DLR or Orange County it would not occur to me or anyone in my family to use 60. Using 91 is automatic for us. I would be curious if there are any commuters out there on DIS who commute from Riverside to OC using 60 as it seems so strange to me and, frankly, out of the way.
In any case I fully agree that 91 is a very busy highway and can be a disaster at peak times. We took 4 hours once to get from DLR to Riverside (40 miles) when leaving DLR at 2PM on a weekday. When we travel to DLR from Riverside these days I borrow a toll lane transponder from by step-father so we can use the toll lane if necessary.
Like all of the SoCal highways it depends on time of day and the whims of the traffic gods.
I would still recommend using 91 even though I am clearly in the minority here. But I would time it to avoid morning rush hour if possible. Traveling from Riverside to OC any time other than in the morning should be fine in my experience. In the evening the traffic flows the other direction.
Just my two cents.