I can honestly say I never work fro GC's as they like the government ask for the lowest bid normally and you see how the government works.
Normally a GC has to guarantee their work for one year after completion and if something does fail the GC points to the various trades that worked on the job
MUCH like Hillery Clinton says she cant recollect and then has the gall to right about her memoirs (called selective amnesia).
If your not sure what to do hire the legitimate plumber watch her or him and the next time you will know if you want to tackle the job or not.
Cast Iron has proven longevity, does not promote fire or smoke and with the longer radius fittings makes for a long lasting quiet safe system that does not sag.
The only thing is make sure the cast even if it is NO HUB CI is not imported
The connections can be either caulked or used with No Hub couplings and NEVER with Fernco (IMHO) as I like the idea of rigid connections not a piece of rubber for integrity.
Considering this piping is going to be installed and possibly forgotten make sure the plumber knows about threaded galvanized rod and Clevis hangers and not a band iron specialist or worse tie wire.
Your home is an investment and you want it as maintenance free as possibe and looking for longevity.
Here is a picture of a NH installation with clean outs at the change of direction and clevis hangers. notice no sagging and how the clamps are stainless steel for a clean professional look.
Every joint can be taken apart if you have to make changes and have to snake the lines in the future