Most speedtest servers are hosted on 1 gigabit/s which means you will probably never be able to get a clean 1 gigabit/s reading from those. That would require that you got the server all by yourself and that wont happen.
We are an ISP that sell gigabit. We host our own speedtest.net server on a 10 gigabit/s. It might be considered "cheating" as the user will only be measuring our internal network. But there is simply no other speedtest server nearby that is able to give consistent good readings. There are a couple that will give you ok readings ("almost 1 gig") but that depends on the time of the day and you might have to try several times.
And no, our transit connections are not congested. However ISPs that do not market themselves as selling 1 gig or more will have no reason to establish 10 gigabit/s at all interconnections. But that also means traffic to them will be limited by the interconnection.
Take a look at any IX member list and notice how many companies have only 1 gbps or slower ports. Our users will never get 1 gig to those guys if the traffic goes that route. Remember there will always be other traffic on the port as well.
However, if a user has traffic to multiple destinations he will usually be able to take full advantage. So it is good for families. You will never be slowed down by what others are doing in your household.