Stoves: Buy new.
Why: Safety first.
Older stoves made for home kitchens don't have the same safety features modern-day appliances do, especially if you're cooking with gas.
Modern gas ranges have an automatic pilot, which means that gas only flows when you want it to. When the pilot goes out, the gas won't turn on. With older gas stoves (and with commercial ranges), gas flows continuously through the pilot. If working correctly, the pilot stays lit all the time.
But what if the pilot light goes out? The gas still flows, which can make the air in your home explosive — literally.
Older electric stoves don't pose the same kind of risk, but they're not as energy efficient as today's models, and the wiring might need to be redone. It's easier, safer, and more cost-effective to go new.