Valuations cost nowt and don't (or shouldn't) tie you to the agency that does the valuation. In fact there is nothing to stop you getting several valuations from different agencies.
However, if you make sure that at least one of the agencies doing the valuation is the same one who valued the upstairs then you will be able to ask them directly about the relative merits of each flat.
In purpose built flats the flooring between each is more often than not made of concrete and thus noise through the floor is not an issue, however in converted buildings like mine there tends to be more noise although now-a-days there are quite often 'floating floors' to reduce noise.
As I live in a top flat myself(I have in fact just sold it)I feel that I am better placed. However, the flat beneath me has a very large balcony and this a useful and private outdoor space.
Please don't ever think that not having steps/stairs to go up is a disadvantage. For many able-bodied older people walking up and down stairs is a good form of exercise. On the other hand if you are on the ground and have a garden that can be an advantage.