PVC vs ABS

I have a house built in the early 70s on top of caliche in Houston. The pipes under the house are the original ABS and appear to have a leak. While we're under the house, should I replace all the pipes with PVC? WHich is better and standard practice now? How can we best maintain our ABS for the rest of their lifespan? Should I keep the pipes under the slab or reroute them through to the attic?

ABS vs PVC is mostly an availability thing; most places pick one or the other. If you happen to choose the other, there may be some available, but the choices in fittings may be limited. As far as I know, there is no big benefit to one or the other.

Caliche and clay, two really nasty things to combine, may be common there, and things can swell and move around a lot with moisture changes. If the piping wasn't installed taking that into account, it could crack and leak.

Typically, abs and pvc are drain lines, and without adding a pump and a sump, you can't really route things through the attic. CPVC is used in the house for potable water, and pvc (not drain pipe) can be used for water supply piping, but must not be used INSIDE the house. Being as hot as it is, I'd not want to run my water lines up there, either...I'd rather run them through interior walls to keep them cooler. Plastic pipes in the attic may not be a great solution...the heat can be significant.

PVC, ABS, it's all the same. Makes no difference, one is no better or worse than the other. If you have ABS, stick with it because changing it out or even changing pieces of it requires special adapters and would be a huge PITA for no reason.