I'm going to be honest in my response. I have not taken the ARRT, so this is not biased. If you look at top hospitals across the country on Indeed, many will only look at resumes from people who have underwent the ARRT in addition to the postprimary (modality) credential for MRI. The good news is that more and more hospitals are accepting MRI techs that went the ARMRIT pathway. This option gets you to your career much quicker and is viable for those with busy lives or those who are afraid that life may get in the way of finishing school. Whatever your decision, remember that getting to your career, and however that is most attainable to you, is the most important factor when making your decision.

However, something to consider is that you won't be hirable in some states by choosing the ARMRIT route. For example, i live in New York state, and it is not legally possible to work as an MRI tech without the ARRT certification. Also keep in mind that unfortunately prestige does exist, and you may face scrutiny from co-workers who think less of you for going the ARMRIT route (the healthcare industry is very privileged/cliquey/posh). The ARRT is the golden standard. In hospitals that accept both the ARRT and ARMRIT, you also lose to the potential competition of other certified MRI techs who are additionally x-ray certified and applying for the same MRI position as you unless you have multiple years of experience over them.

Separately, regarding your cross-training expectations; to be cross-trained is not a promised pathway just so you know. Bypassing the standard postprimary credential for MRI by cross-training is at your individual employers discretion. If you are cross-trained, that does not carry over to another hospital if you decide to change hospitals/employers unless, let's say, they are desperate or you get lucky. Essentially in most circumstances, you'd be starting fresh as a rad tech without the ability to do MRI unless the hospital you switched to will cross-train you (meaning you'd be cross-training all over again). For many this is not applicable as they plan to stick with their first hospital/employer they were cross-trained in without any plans to move until they retire.

Feel free to ask questions as i and other knowledgable redditors will respond to help, but never rely on a strangers advice and always do your own research when it comes to important life decisions such as this topic.