But so, why CITIC or China Merchant's?
again, my experience in Beijing.
They both have modern backends and SOP practices. CITIC is arguably bigger than BoC and handles a lot more international business.
CMB is the most modern of the big 5 with great customer service. It's also the most outward looking as it sets to differentiate itself from the rest of the pack. They were the first Chinese bank with an English customer service and website for years before the advent of apps.
As far as ICBC, I don't know anyone that opened or uses an account there by choice. They're very much tied to corporations (salary payments, corporate accounts etc..) and they excel at it, but when it comes to personal accounts, they've got the monopoly on "meiyou" and "buxin"
Now of course, like with anything in the big silly, your mileage might vary. It also depends on whatever 16 year old is sitting behind the counter, if they had a bad day etc etc etc... you get my drift.