Which approach do you believe would provide the best fit to

Question

Question: Consider the following data:

Y          2           3           4           5          6          8          11          15          18           23            29              37              47              59              70

X          1           2           3           4          5          6           7            8             9            10            11              12             13               14              15

Which approach do you believe would provide the best fit to these data: monotonic regression or a quadratic spline with the knot determined from inspection of the graph? Use both approaches and compare the results.