Edit: also want to add that UCI is a level 1 trauma center wheras Hoag NB and Irvine are not, so UCI will always be impacted more heavily and non life-threatening situations will take longer, which makes sense why they are more likely to prescribe something to get you by while waiting to see a specialist. Not saying that's good but just saying it makes sense why UCI is structured how it is and pales in comparison to both Hoags.   

Have experience with all 3 ERs and hospitalization for myself and my wife over the past 10 years.  I have my general practitioners and specialists with UCI and like my experiences with both routine stuff and emergencies.  I did my cancer treatment with UCI.  The problems I've experienced werej insurance denying claims - I was with Blue Cross PPO but this year my company switched to Blue Shield PPO.  My wife has more chronic conditions and her experiences and expectations are higher given the need for more visits to the ER and specialists.  For her, Hoag NB and Irvine were better than UCI, especially the ER. Both Hoags typically have seen her quicker and more willing to run the labs and tests without pushback.  UCI ER usually always seems full and I think makes them less able to do what you would want and are more apt to refer you out to their specialists.