Starcraft – way to turn off auto save

No. There isn't. Especially not on the ladder. Then you could say "Block everyone else in the top 200", and you'd never lose! (if you were good enough to beat everyone else)

When you play online you don't have much control over the map you will play. You can veto some maps off but in the end, it doesn't really matter whether the map is really played a lot or not, just your personal preferences.

In tournament, a popular map choosing technique is that the first map is decided either randomly, or every 1v1 starts on the same map. In Starcraft 1 Lost Temple has been chosen like this a lot in the early days (later on, it has been judge a little imbalanced because blocking the ramp gave the terran players a slight advantage).

After the first map, either the winning (rarely) or the losing (much more often) player would decide which map is to be the next. I'd say that most of the time, a 4 players map for a 1v1 is prefered since it gives each player much more territory to expand. Sometimes, they will choose "Steppes of War" in a "I want to rush you" fashion since it is the map where the spawning spots are the closest of the whole map pool.

So, on Battle.net, the maps are random so personal preferences don't impact the game much. Some maps are better for some races or some strategies (large choke points = harder to block = easier to rush).