It's more proper today to just refer to the speeds of a bike as the number of cogs on the rear.
So you are talking about bikes with 7, 8 and 9 speed rears? Why? Why not get a more current 11 speed bike?
Essentially you need to state how much money you are budgeting for a bike. And will you budget more for a new bike under warranty?
You can go up a hill on a 7 speed bike just as well as a 11 speed bike. Providing they have the same low ratio gears. More speeds give you more options in between the low ratio and high ratio.