I am thinking to start a new VA which will operate mostly jet airliners for passengers service. As a first step I am planning two have two hubs. One will be Athens Intl (LGAV) and I am asking your opinion about which one you would like as second.

There are several factors to consider when selecting a hub, and a few more when you're doing it with a sim.

1.  Traffic.   You don't want to fly somewhere that is going to result in a 6 hour traffic delay!

2.  Location.  Depending on your fleet, you will want to be somewhere semi-centrally located.  (And in all fairness, even if you've got a fleet of 777s, you'll probably want to be central just to save on fuel!)

3.  Sim hubs...find somewhere visually attractive, preferably with some add-on scenery available for anyone who might want to enhance it a bit.

Good luck!