I haven't played too many of the stock maps, maybe about half in total. Personally I find the random map generator generally does a better job (though the random part can screw you over...) and that's why I and most other people online go with them. Gateway is possibly the most popular of the premades, but personally I don't think it's anything special.
Now, I love the work of a lot of the community mappers, including DirtySanchezz here. That's not to insult Ironclad; we have the benefit of knowing how the meta-game of Sins of a Solar Empire is played and we have a good sense of how a player will be able to orchaestrate their offense and defense in specific situations. When IC was making their maps before the game's release (and LONG before plastyles matured), they were mostly taking a stab in the dark.
