What is the best of given hashfunctions? In our exam on algorithms there was a question, where given 3 hashfunctions we had to chose one and explain why it's the best.

h_1(x,i)=(x+5*i) mod 1000
h_2(x,i)=(x+17*i) mod 1000
h_3(x,i)=(x+32*i) mod 1000

I am really unsure about this, but I suspect that it is the second one, because it can "hit" more values. If I choose the first one for example, I will be hitting the same buckets over and over (if they are full). Question seems quite simple but my math lecture on this has been a long time ago.
The question is not well-defined, since its unclear what you mean by "best". 

I suspect that the intended answer is what you said and that you are using open addressing. Then, for a given $x$, $h_2$ would eventually return all possible values in $\{0, \dots, 999\}$ (since $17$ and $1000$ are coprime). $h_1$ would only return $\frac{1000}{5} = 200$ distinct values, and $h_3$ would only return $\frac{1000}{\textrm{gcd}(32,1000)} = \frac{1000}{8}=125$ distinct values.