In a sequence given to find the next number that follows what happens if we can see 2 different ways to produce the next number? Given that the approach is based on inductive reasoning, unless the sequence is some specific well known math sequence how do we choose which is the most sensible choice?
Example:
If we have:
$3, 6, 18, 36, 108, 216, X?$
We could claim the following:
Since each number of the given sequence above is exactly divided by the 2 previous ones i.e. 18 is divided exactly by 6 and 3, 36 by 18 and 6, 108 by 36 and 18 and 216 divided exactly by 108 and 36 then $X=432$ since it is exactly divided by $108$ and $216$
Since we have $6 = 3*2, 18 = 6*3, 36=18*2, 108=36*3, 216=108*2$ then $X=648=216*3$
Is there some reason (2) is more valid than (1)?
Unless you define exactly what you mean by sensible, the question you're asking isn't well-defined. The Fibonacci sequence is as good as any sequence starting like $\{1,1,2,3,5,8,13,-9383948,...\}$. In your case, $X$ can be absolutely any number and there would be no objective rule for ranking the options.
You can create a particular definition of sensible. For example, you could say "If it's an arithmetic or geometric sequence, those are sensible choices". Then you could use that rule to distinguish different options. But then your question answers itself: to rank the options you need to create a subjective rule to do that. The validity of your rule is again, subjective.