Having lived for most of my life in Orange County, I have quite a good perspective on the difference between the two counties. For me personally there is simply no comparison; Los Angeles is far superior.
Orange County is great for those who want to have a family in a safe area and put their kids in a good school district. However, Orange County is rather boring. It's basically a bunch of strip malls, chain restaurants, tract houses (which all look the same, just cruise through Irvine if you don't believe me). It's the epitome of all things suburban, which to me is dreadful. Living in the suburbs (like OC) means that you've given up and settled for a comfortable live and a white picket fence around your house and are ok with driving a mini van while living in Los Angeles (to me) means that anything is possible; fame, fortune, immeasurable wealth. It's all within reach in the City of Angels depending on your ambition and willpower.
Los Angeles is very urban; you can already see the skyline of the glorious tall buildings as you enter L.A county via the 101 Freeway. Los Angeles offers more in terms of culture, entertainment and style. I like the fact that it's a bit dirty, gritty and dangerous. O.C is almost too safe, too boring.
The biggest difference I noticed when I started going to L.A is the need to parallel park. I hardly ever have to parallel park in OC and to be honest, I still don't know how to parallel park so what ends up happening is that I keep on driving aimlessly for hours without being able to park! I don't see how it's possible to parallel park on Sunset Blvd because you need to "reverse" in order to parallel park and how can I reverse with all of these cars behind me?!
Another major difference is that streets such as Sunset Blvd and Hollywood Blvd only have two driving lanes; the third one is used for parking only! This can be very confusing as I found myself often driving in the third lane and having people honk at me.
Another thing I noticed is that you cannot U-turn in L.A!!!! O.C has nice big wide streets with lanes with plenty of left lane turns where you can bust a U. In Los Angeles, you either have to go around the block or bust an illegal U-turn, it is very complicated. If you plan on driving around L.A you definitely need a GPS system. One wrong turn and you can end up in a really sketch neighborhood.
Plus the roads are much more curvier and narrow in Los Angeles. Orange County has nice wide streets whereas L.A's freeways are so narrow; I get quite scared driving there. Sunset Blvd also has so many twists and turns; especially around Beverly Hills. I found it very hard to navigate that area.
Even with all of the complaints I still much prefer Los Angeles over Orange County. There is simply no comparison.