There isn't a "best" one.
For every method with a real edge, the "best" R:R is the one that makes the most of the edge ("has the highest PF" or however you measure it).
There are methods that are profitable with a 1:1 ratio but lose money with higher ratios, and there are methods that are profitable with a 3:1 ratio, or higher, that lose money with lower ratios.
It all depends on what type of trading and method it is.
You find the answer from the method.
One of my most successful methods is only about 0.75 reward to 1.0 risk (it comes up often), another is nearly 4.0 reward to 1.0 risk (that one's aimed at catching the beginnings of new trends, and has a lot of false starts and a few big winners, of course).
Given the huge difficulty of coming up with methods with a genuine edge, and the great ease (comparatively!) of backtesting them to investigate the ideal target/SL ratio for them, there's no point at all in starting out "in abstract" with a defined R:R and then trying to find a method that fits it.
That would really be putting the cart before the horse!