You should always use warped. 90% of runs use warped forest instead of bastion. Bastions usually take longer than warped forests. How you explore a quadrant is up to the runner, I find that exploring to about 200, 200 in a quadrant works the best but that is just what I think. If you search the whole quadrant and can't find anything it probably is an unexposed bastion. Fortresses are larger than bastions and if a fortress is in your quadrant you should be able to find it quickly if the terrain isn't trash.