I encourage people to use that "User" render type and learn what all those settings do and about what each costs in render time. Then you can get max render speed for whatever quality you're willing to wait for.
 
Some render engine settings that slow you way down, if your materials need them:
   * Blurred transparency
   * Blurred reflections (very slow)
   * Optimize volumetrics
   * Caustics
   * Depth of field 
   * Soft shadows (very slow) use the settings in the Light and Shadow editor for speed, not AA,

Lighting that's slow:
   * Volumetrics
   * Soft shadows
   * Advanced clouds or terrains

Objects:
   * Poser imports with the usual huge texture files (you can always make those smaller in Photoshop or another image editor.
   * Complex imported buildings and environments

Also, you don't need to make huge sized renders for posters and such. Use PhotoZoom Pro to instantly upsize your 1024 or 2048 renders. I've gone up to 6K pixels with no visible loss of quality.

HTH