Start with the Harris County Simulcast (01-34) for HC agencies, and whichever 3-0x site you are geographically in for HPD/HFD. If your radio is not Phase II, your only option for HFD/HPD is 03-05 as it is the only site that carries them in phase 1.
The non simulcast sites in HC are typically only used for transient talkgroups with a few exceptions.
EDIT:Since you have an SDS, use 3-1,2,3 or 4 depending on your location. I would not bother with 3-5.