I think both forms of cardio are great... but it ultimately comes down to diet. You can't spot reduce, and I know for me as well as others the fat on your abs is generally the last to go. I'm cutting right now and i've lost about 4 pounds in the past 2 1/2 weeks from a tighter diet and cardio 6 times a week.
Also, I've been talking to a guy at the gym, and he's been swimming laps after his workouts for the past month and says he gets a better cardio workout than running... if that counts for anything
I remember one of the male swimmers at the USOTC back in 98-2000 era that was taking in about 4000+ calories a day of anything and everything and he sure was ripped to shreds by doing tons of laps a day.
But I guess both running and swimming will burn fat but I guess it does depend on your diet and on your intensity...mind you this guy was swimming miles a day at high intensity.
good cardio yes good for fat loss no
i read somewhere i can never remember where that your body will keep fat to keep warm if subjected to the colder water temp. i dont recall ever seeing a swimmer with descent muscle mass and being cut. i could be wrong