[Outwest34au]

My peference would be mild steel for the headers if you are going to handmake them or if they are long and dangly going to collectors for side pipes. Less prone to cracking under high heat but all that crack risk is dependant on how tight the bends are. As for the integrity of ceramic I dunno, looks pretty, sounds perfect in theory. But if I can't afford it on the day I wouldn't be grumbling about VHT pressure packs at all.
The average mums car that just does short runs and never gets "REALLY' warmed up would definitely see a longer life in the horizontal underbody system if stainless. And by warmed up, I'm not talking racing, just allowing a long enough time to get full heat soak to the exhaust. Mufflers towards the rear will obviously gather more condensation over time than forward mounted due to the time it takes to heat soak. Heat soak is different than just thinking you have ?x? amount of degrees C blowing thru it. Exhausts inherently are not de humidifiers.
If I had one tip to offer for an "infrequently" driven car, hmmm, drill a 1/16 or better 1/8the inch hole at the low point of the muffler. Might sound silly, but look under the rear resonator on most bog stock factory family cars and you'll find that hole. Then observe the neighbours car and you'll notice the odd drip.

My 2 cents worth, which rounds down to zero nowadays we know.
Cheers