[Alneyan]

Assuming we are talking about the vanilla game: Dreadnoughts all the way, unless facing a Religious opponent and/or being involved in gamble battles. In reasonable battles, where both fleets aren't sending in hundreds of warships each, the defence penalty of the Baseships can be a killer, especially when faced Dreadnoughts set at "Maximum range" (even if the Baseship can close in, they will have 1% to hit you at range 8, assuming equal training and all bonuses to offence/defence), while you have a nice 35% chance to hit them at range 8. The basic odd to hit at range 8 with all defence/offence devices is of -5%, hence the 35% for a Dreadnought against a Baseship.

If you have reached the stage of the game where only figures matter (NGC and Roanon, they who have lost salute you!), I will go with Baseships, since the battles will be closer to slaughters involving many, many vessels, and ship versus ship considerations are much less important. The only exception would be if I used a strategy of causing mass riotings, where speed would be more important than the number of APBs my ships can use (a planet isn't going to be that much of a threat). But at this stage of the game, your opponents are likely quite warded against wild Warp Opening, making the riot runs much harder to pull out.