It's all in the gamemode, and how you want the map to play out. There is no real better speed,as long as the map is designed with fast or slow gameplay in mind.
I prefer a longer map as you can get some defences down that won't be irrelevant within a few minutes and also it isn't just a mad dash to an objective it's more carefully planned out. And having the whole team working to get past a well-made choke is actually quite fun sometimes.
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