Which is best in the long run?

filtration is more imporant they are hardy fish so will be happy from 19 c anyway but the filter will prevent ammonia which will definatly kill the betta fast and if it withstands it give it diseases. have filter run a week then add fish., feed bloodworms do a 20 percent waterchange weekly. make sure its dechloriantor water or it will burn the fish and prevent filter working as it should.