First move choices  

Here are the possible opening moves on a 9x9 board, in roughly descending order of popularity from a set of pro games (largely taken from Gobase).

[55]

5-5 opening  

The 5-5 point seems to be the most popular opening.

[34]

3-4 Opening  

There are many choices after 3-4, but of these, h-k have appeared only once in the set.

bugcat: For what it's worth, a dan player once told me that they had never lost on 9x9 against an opponent who opened with 3-4.

[44]

4-4 opening  

Choice a appears about twice as often as any other choice.

[53]

5-3 opening  

Choice a is about twice as popular as anything else, and f appears only once.

[54]

5-4 opening  

Choice a is more popular than the others.

[33]

3-3 opening  

No doubt other choices are possible as well.