Emergency vs Critical Care nursing

You can't really say one is harder or more stressful than the other. You are comparing apples to oranges. Each specialty comes with it's own challenges and stress. I have worked both and there are things that I like about the ED and things I don't like. The same for the ICU.

If you think you may want to go to CRNA school someday, I'd say ICU. If not, well, which one appeals to you more? They both have their pros and cons, so it may just depend on your personality, and more importantly, the job market.

How do you like unpredictability?
Even though the ICU patients are usually sick, there is a certain predictability in how your day moves.
You get report on your 1 or 2 patients, do vitals, assessments, meds, check new orders, chart etc. ICU has a rhythm and structure to the day the "creatures of habit" like me prefer.
ED is more unstructured. You will need to be prepared to pick up new patients, deal with varying levels of acuity. If you get stressed when your carefully planned mental agenda gets reshuffled then ED will be harder. If you can handle unpredictability and hate routine, then ED is for you.
Both give you excellent nursing skills, though if you are a new nurse, look for one willing to give a thorough orientation.

Great question. I have experience in both areas - as a clinician and as an educator.

I would recommend ICU to gain a better appreciation of "nursing" practice. The ED is a great place, but in the US, it is really centered around "medical" practice and "medical" interventions. ED nurses do a lot and many are highly skilled but their work is always carried out under the immediate supervision of a physician. Scopes of practice establish the basic parameters, but the ED environment also structured to be compliant with current reimbursement practices... which require direct physician involvement. ED nurses enjoy the episodic nature of their patient care and usually wilt when faced with the more tedious aspects of patient recovery - LOL.

In ICU, on the other hand, patient care is still highly interdependent (nursing & medical) but nursing practice can also flourish because much of the patient care is focused on goals that are completely within the realm of nursing practice such as emotional support, education, physical conditioning, discharge planning, etc...

If you're keen on working with machines that go 'bing', (ala Monty Python), ICU is the place for you. ICU nurses enjoy working with all sorts of clinical technology.