Verb (type 1): to interest.
Kiinnostaa is both the infinitive form and the 3rd person singular of this type 1 verb. Here it is in 3rd person singular to correspond with kumpi, an interrogative pronoun which asks ”which one” of two options. (See the inflections of kumpi here.)
The headline asks people which they are more interested in, Krista (Finland’s 2013 Eurovision Song Contest contestant) or Leijonat (Finland’s international hockey team) both of whom had big nights yesterday. Sadly, neither won.
Kiinnostua is another verb which means ”to become interested,” ”to become intrigued” or ”to become fascinated.”
Kiinnostus is a noun which means ”interest.”
Kiinnostava is an adjective which means ”interesting.”