Well, I am not quite sure. The romanian civil officials are talking about a multirole fighter. the militaries are somehow silent. the best option as price/quality I consider is Gripen followed by F-18.
I believe that the fighter should be able to do the following (although no official statement yet) :
fist, defending romanian air space as interceptor or dogfights
second, performing decent strike against enemy
third, limited naval strike or antiradar attacks
I am assuming that because at this point we have no decent planes. there are some upgraded Mig-21 but their performances is limited. Some upgraded Iar-99 (light attack/training plant, L-39/Hawk class) can be used for antitank attacks
4 bilions euro with training and all stuff
If Romania does not currently have any "decent" planes, then multi-role aircraft would seem to be the way to go.
Not too surprising that new aircraft are needed really, given the time, money, effort, etc that has been needed to bring Romania more in line with NATO and EU forces.
Of the shortlisted aircraft, any could act as an air defence fighter, some admittedly better than others, with Eurofighter likely being the best.
However, given how most air conflicts seem to be unfolding with current equipment, tactics and forces, it would seem more sensible for Romania to have a good strike aircraft that also can do air defence, as opposed to the other way around. Having said that, I would not consider the Eurofighter Typhoon a good choice for Romania. If Romania could afford to have 2-3 squadrons of different types of fighters based on roles, it would be a different story.
That would leave the Rafale, F-16, F-18 and Gripen. IMV the Rafale would likely be eliminated due to cost and commonality issues, unless France and/or Dassault offered very favorable rates and offsets for the purchase. Personally I do not think the Rafale bid would be "sweet" enough for Romania to become the first foreign operator of the Rafale. Could be wrong though.
That would leave either the F-16, F-18 or Gripen. Here it is difficult to tell which option would be best, as any or all of them could be new, or secondhand. In terms of overall capability and service life, the best option would likely be new F-18 E/F Superhornets or perhaps late block F-16's. However, the cost could exceed the available budget and the timeframe might be as issue as well. By way of example, the Royal Australian Air Force (RAAF) is set to get 24 F-18F Superhornets in approximately the same timeframe, at a cost of ~A$6 billion IIRC, however that also includes costs for training, support, weapons and operations for ten years. Romania might be able to get 48 Superhornets for ~4 billion Euros, assuming that figure did not include ongoing operations and support costs, just the initial acquisition and training costs.
On the other hand, if Romania is just looking at the 2nd hand market, it is hard to say. Any of the three could be picked up since there are some surplus aircraft available. What is less certain is if any of the aircraft what are available would meet Romanian needs in terms of service life and capabilities.:unknown
It will be interesting to get more information on the available offers, as well as what Romania is really looking for in terms of capabilities.
-Cheers