Victory in Brazil will mark a second consecutive World Cup triumph as La Roja look to become the first European nation to win the coveted trophy in South America.
"The individuals are superb and the way they play is very clear so youngsters can fit in," Martinez told The Guardian.
"Now they have the extra element of Diego Costa, an ex-Brazilian who you can imagine is going to bring a lot of spice.
"Against Brazil last summer they needed to find a way to get out of their own half and they can add that to their play now with Costa. I do feel Spain is still the team to beat."
Costa is expected to start for Atletico Madrid in tonight's Champions League final against city rivals Real Madrid.