whats the strongest ring metal i can get?

Hi, this is a slightly difficult one, strength is different to scratch resistance, and tarnishing is something completely different again. I'll break it down into 3 seperate answers:

Strongest - Tensile strength - lack of malleability - in precious metals, Platinum is the strongest and densest.

Scratch resistance: 14kt gold is generally the most scratch resistance of the yellow gold materials, Rhodium is the most scratch resistant of the white metals - this means, any carat WHITE gold alloy, with a Rhodium plated finish will not scratch as easily as yellow gold, and Platinum scratches easier again.

Tarnishing: This is dependant on the alloy used, the purer the alloy (higher the carat gold) the less tarnishing, because gold & platinum are all NOBLE metals they are by the very definition do not tarnish. When we alloy a precious metal we use silver & copper (and in the case of white gold generally palladium) to strengthen and change the alloy to what is our desired caratage, 18ct is 75% gold, the rest is silver & copper, 14ct is 58.5% gold, 9ct is 37.5% gold, tarnishing usually occurs in 9ct, as it is mostly copper & silver alloy, and is much more reactive.

So, you have 3 different answers almost.... no single metal will fit the bill on all, unless you perhaps use tungsten steel which may be the best match for all 3. However, most jewellers do not work with steel or alloys of steel. 

I hope this helps.