The answer is:
It depends, it is largely a matter of opinion, and is not static but changing with each update.
Laserbite is a good option – so far – throughout the game, and in most situations. Most people seem to agree on this.
In many situations it is better to have several planes, even if they are not as fully developed, rather then put all credits into one plane.
But again – there are no definitive answers: To get to higher levels, you will need most of the planes, but think twice where you put your upgrading credits.