Europe

How long a trip? Focused on one or two places, or is this a “grand tour” kind of thing?

I can’t really recommend one over the other because out of those countries I’ve only been to Great Britain and Ireland. All I can say is that if you do end up going to Ireland I strongly recommend that you rent a car and get out of Dublin. There are neat things to see in Dublin but you can pretty much do the best ones in a day IMO. Otherwise, Dublin kinda sucks and is really expensive, the best things are out in the countryside and you will need a car.

Ireland, you can cover the whole place in 5-7 days

Really depends on what you intend to do? History; nightlife; nature; culture; restaurants; or active?

I know people here sometimes hate on London as a beginner's trip. Honestly though, you have to do it at least once, so do it now. 5 days is perfect, especially if you add in a day trip to Windsor, Bath or Cambridge.

Stay at the Nadler Soho. You are in the middle of everything -- in the most interesting area of London.

Take the significant other shopping on Oxford Street (especially Selfridges). Go see Book of Mormon. Eat at Hakkassan Hanway Place.

Take the hop on hop off bus. See the tower; the London Eye; the British Museum; the Churchill War Rooms; Buckingham Palace. Once you get the lay of the land, take the bus or tube, or black cabs (London taxis are best in the world -- they destroy Uber).

Buy the Lonely Planet Guide to London. Use that to plan your itineraries. No need to go on a guided group tour.

Viator is an OTA -- so they sell tours from various vendors. Good overall source for tours.