A general rule with aircraft is to not get more range than you need. Longer range costs more money to buy (and maintain, and (usually) to fuel and etc.). So, if the routes you intend to use this plane on are under 2000nm, then buy the cheaper one. The only reason to get longer range aircraft is if you indend to use them on longer routes in the future (however, with an A319, you probably won't be planning to upgrade in te near future anyway).
Your strategy seems a bit strange. If you are based in Europe, you should focus on short haul (as in below 500nm, certainly less than 2000m first). With only 30 routes, you are nowhere near exceeding your short haul limits. Buy the shortest ranged A319 (or even A318) and fill the short routes. If in America, similarly, you could create more short routes. If you are based somewhere like Africa (where I could undestand you wanting to fly somewhere bigger), I would still advise buying a number of small planes and servicing smaller airports there, even at 30 routes, or upgrading the aircraft on big routes and moving the small planes to smaller airports.
You should keep in mind that shorter flights are far more profitable than long ones. You will make much more on an A319 doing short haul routes to small English airports from London than an A319 flying 2 0.5 routes to large US cities.
