Is there any way I can create a dwarf fortress world with no brooks, or at least fewer of them? Some specific settings in worldgen, maybe? I like to use bridges as chokepoints, and the streams as barriers to invaders, but it's very difficult to find a good embark site with anything other than a brook.
According to the DF Wiki, rivers need a fair bit of elevation (300 and up) and rainfall to form. Creating a world with high elevation and rainfall will result in more rivers. The article has quite a bit of info on creating worlds with custom parameters.
A bit of terraforming could also go a long way. A moat is an excellent way to prevent attackers from hugging the walls, making sure they are at the optimal angle for marksdwarves behind elevated fortifications. Carving a fortification into the map edge should allow for infinite drainage, so you can still have moving water in your artificial river.