Stainless tanks got a bad rap for a long time.
In the earlier days many were made from inferior grades of metal and the protocols of welding techniques weren't well established, (proper filler rods and gas usage,) as a result, over time many developed leakages at the welds.
If any water was present in the tank, the Sulphur in the fuel would react, creating acid which attacked the welds.
For fuel they need to be welded not only using TIG with gas surrounding the weld area, but they need gas on both sides of the weld.
With proper construction a stainless diesel tank can give very long service
Aluminum can make an excellent tank, no doubt about that.
Can you keep salt water
off of it? If not, there will be issues.
Can you drain it down to the last tablespoon? No matter the material any fuel tank
should be so configured and have a valve with an attached hose that can be tie-rapped up out of the way, its end above the tank.
Every now and then stick the hose in a bucket and drain out some fuel.
For a fuel tank
, if cost is not an issue, a Monel tank is superior to either aluminum or stainless.
A plastic tank? No thank you, at least not any that I've ever seen.
A previous post mentioned water tanks, stainless makes great tanks, copper makes them better.
You will have healthier water even just using copper piping for the water lines.