We did this trip + London in October of this past year. It's a great time for it.
I liked Scotland more so than Ireland personally but I'm a scotch drinker so I'm a bit biased. Edinburgh, St Andrews, and the highlands are must do's. Our favorite part of the whole trip was renting a car and driving the scenic route from Aberdeen to Dufftown(scotch Mecca). The country side was changing colors and was BEAUTIFUL and we timed it to where we could hit up a Glenlivet distillery tour at the end.
I'd like to go back and see(drink through)some of the other parts of the country though.
Ireland was fine, just not as captivating as Scotland in my opinion. Dublin is very much a modern city but it has historical touristy stuff to do/see. We saw a lot of homeless/loitering which turned us off. I will say that they have something like 30k bars and they are busy every night if he week if you're into that sort of thing. Cliffs of Moher was pretty but it's a bit of a hike.
One recommendation, book a hop on/off bus tour if you go to Dublin or Edinburgh. The ticket is good for 1-2 days and we used it as a taxi during the day. Saved some cash and you go to parts of the cities you might miss if you're on your own.
“There is no red.
There is no blue.
There is the state.
And there is you.”
“As government expands, Liberty contracts” - R. Reagan