HI Neil,
Welcome to IceInSpace
An 8" DOB is an ideal choice for a first scope.
10" even better if you can afford it.
Beyond that size weight and moveability become an issue.
The best scope for you is the scope you (and your daughter) will use more often, so ease of setup and transport is important.
Bintel is a great place to start your hobby.
People there are friendly and helpful.
If you can get to their Camperwell store, you can see and feel the scopes before you buy. This is a big plus.
Good luck with your purchase decision(s)
and keep asking questions
Cheers
Allan