Contrary to some expectations, South Korea has not declared a winner in the FX Phase 3 tender to supply the Air Force with 60 new fighter aircraft to replace existing F-4 and F-5 fighter jets. A previous round had also not been won by anyone.
Since Boeing's F-15 Silent Eagle (SE) was revealed to be the only one to have submitted a bid that came below the maximum of 8.3 trillion South Korean won or $7.2 billion limit set by South Korea, the F-15SE had been expected by some to be declared the winner of the competition.
The other two candidates, the Eurofighter Typhoon and F-35 Joint Strike Fighter, exceeded the limit and were therefore by law not eligible to be selected. This made the F-15SE the only candidate that could have been selected by South Korea.
South Korea's Defense Acquisition Program Administration (DAPA) opted to
restart the FX Phase 3 Project from the beginning. This will postpone
the acquisition of the aircraft and may include some changes such as
raising the budget or reducing the number of aircraft to be bought.
This turn of events indicates South Korea's preference for the F-35, although to a certain limit. Even though the F-35A is still in development and experienced some problems, the fact that it will serve in significant numbers with several Air Forces gives it a sort of insurance for the future against potential difficulties.
The F-15SE is derived from the F-15 which is already in service in South Korea, but it's partly a paper project which still needs lots of development. There is also a real chance that South Korea would have been the only country to use the F-15SE which is not a good thing.
The F-15SE has been designed with low observable (LO) features, but to a lesser extent than the F-35. An important issue since LO is set to become much more prevalent in the near future, including in the Air Forces of Russia and China.
The Typhoon is ready to contribute right away, especially in the air-to-air role, but doesn't have some of the fifth-generation capabilities that the F-15SE and the F-35 especially possess.
South Korea is one of those countries that favors the United States to a certain extent for strategic reasons and the Eurofighter was a longshot to win the competition despite their efforts.