I lived in the U.K. for eight years before moving to Ireland where I’ve been for eight years (before that it was Australia and NZ).
The U.K. is cheaper for most things - food, utilities (particularly mobile and broadband plans), clothing, makeup, perfume, electronics etc The Irish retailer doesn’t just want their cut, he also wants your tears. The courier actually gave us chocolates last Christmas and made a special trip for my dining room lights Christmas Eve morning. Google translate and amazon.fr and Amazon.de will be my new best friends.
The Irish are friendlier, but the British are more accepting of other nationalities/ cultures (perhaps too much in some places). A friend was told recently she needs to be more Irish to succeed professionally here; she’s Australian. Another friend was told off for being here and taking Irish jobs. She said it was somewhat ironic given the Irish reputation for migration.
The British are generally more organised (though Brexit is not a good example). A British tradesman will usually turn up on the day, the Irish could be a week late. This also applies to dealing with any company or department.
I really appreciate the way the Irish mourn someone’s passing. I’ve been to the funerals of people I’ve never met here. Like my colleagues sister in law or my husbands boss’ mother in law. It seems to be ‘the done thing’. The British largely ignored a death professionally. I actually got a written warning from my U.K. employer for taking time off for my my great grandmothers funeral as great nana wasn’t close family 
. I’ve also been to more weddings, communions and christenings here too.
The fixation on honours degrees is definitely true, but it appears to be a more recent thing. So are cars. We’ve purchased all of cars in the U.K... and then paid a fine to Revenue each time of about €3,000 each time (it’s called VRT, it’s compulsory but supposedly not an import tax). We still save money and get a better spec car. Going out is more expensive, for a meal or drinks. It rains more in Ireland.
A lot more.
Where you live is definitely important in Ireland, and state supports are much more generous. Primary and secondary education is almost exclusively religious in Ireland. University education is much cheaper than the U.K. - certainly not £9,000 a year.
The Irish is generally up for a good time, and work tomorrow isn’t a good reason to opt out. The British appear to struggle more with holding their drink, maybe the Irish have stronger genes.
Events are better in the U.K. Festivals, shows, local things run by your council etc are better organised, better value etc. The Irish can claim it’s economy of scale but it’s not, as NZ is a similar size and still delivers good quality, well resourced events.