The best exercise is the one you'll stick to. If you don't like running on the treadmill then don't do it!
If swimming is your thing, go for it!
Now, if you're talking about fine tuning. Adding in some weights is really going to help you lose inches, tone up and you'll look smaller even at heavier weights. But just doing swimming in and of itself is a GREAT start. Right now work on picking something that you will enjoy and can do consistently. Later work on the fine details.
About your stomach, though. You can never spot reduce. Pilates etc will tone up the muscle underneath the fat but in order to reduce fat you have to create a calorie deficit. It looks like you're pretty close to your goal so it doesn't mean that you necessarily have to lose a lot of weight but if you were to strength train you could work on decreasing your overall body fat, which would in turn decrease your belly fat. Unfortunately, it might just be that your belly fat is the last to go (totally normally, unfortunately
) and that's why you experienced having a belly while running before.