I commute from Moreno Valley to Anaheim. I agree with what everybody else has posted. Whichever way you come into OC is fine. The 60 to 91 is probably the shortest, time-wise and mile-wise. HIt Moreno Valley late morning/noon, after the rush hour. Whichever way you come, there is a lot of freeway work going on: Here's the highlights:
(If you take the 10 to the 215-South, there is freeway widening thru Colton along the 215 between the 60 and the 10.)
Back to the 60 to 91 route:
Freeway widening along the 91 thru downtown Riverside for a couple of miles, starting at the 60/91/215 intersection. After you make the transition to WB 91, start merging over a couple of lanes so you can continue straight. The sudden lane-ending confuses drivers and can cause a bottleneck.
More freeway widening: in Corona from the 15 to the 71.
Cal Trans is re-working the WB 91 Tustin Ave off-ramp, so WB traffic can slow suddenly as you approach the 55 transition.
Just a word about the express lanes on the 91: Avoid them. You need a pre-existing account and a transponder. There are no toll booths. And there is a CHP unit assigned specifically to the toll lanes during the day looking for speeders and vehicles without transponders. You can figure out what that means. The "free" portion of the 91 thru Anaheim canyon is nice and wide anyway.
Also, like Executive wrote, you can take the 55 south instead of the 57. If you do take the 55, get off at Katella Ave and go west to D-Land. Katella is a 6-lane "superstreet" (wide lanes, timed signals) which will take you straight to D-Land. I prefer that route because the 57 is so congested during the day.