as others have said I’d be a bit wary of basements as they can be cold, flood, attract mould and damp. They also can be a bit dark.
Ground floor flats don’t have any real issues as far as I know that are different from general flat v house issues.
Lots of people like ground floor because of the accessibility, particularly if you have kids or might do later on. Some people say ground floor flats are more prone to break ins, I don’t really understand this argument because all houses have a ground floor and no one avoids buying a house because it has a ground floor.
be a bit cautious with a shared garden as you’ll be right next to it in a ground floor flat, so if your upstairs neighbours are using it they might be able to see you/disturb you and you won’t have any control over how often/late they are in there.
As others have said, be a bit wary of conversions as noise and tobacco/cannabis smoke tend to travel between flats more than in purpose built flats. In purpose built flats try to avoid ones with lifts if you are going for ground floor as lifts push the service charge up and you won’t get the benefit.
share of freehold is good, but longer leases aren’t terrible and should let you have dogs as long as they don’t cause a nuisance. Make sure the service charge is reasonable and the ground rent doesn’t increase.