Best swimming style

If you are new to constant swimming training routine I suggest that you begin with Breaststroke style. That way you'll develop the basic skills of swimming. After you feel comfortable enough you can move to front crawl which is a bit harder but will make you stronger than breaststroke.

Breast stroke is the easiest and usually the first style beginners pick. However, it could increase lower back pain, especially for women who are more naturally prone to them in the first place.  Front crawl is more strenuous, and therefore more aerobically effective, and keeps you in better shape (or promotes weight loss if that's what you want).

One way to deal with the back problem in breast stroke is using a snorkel (a tube that sticks out of the water allowing you to breath without taking your head out), thus maintaining a straight back throughout the swim.

The best swimming style is the one you can keep to a regular routine, so basically you should pick the one that's good for you. Whatever you choose will give you a cardiovascular workout.

The butterfly

I think the fact that you can do free-style for the longest, and since you use many muscles while swimming free-style, it is a very good choice.  However, I think that switching between strokes is probably the best, because you'll be allowing certain body parts to rest a bit while working others more... and you'll be working the greatest variety of muscles in one workout. 

the best stroke to keep your body fit is front crawl witch makes your bicepts and claf muscles stronger. if u r just starting in swimming then the best u can do is just 2 get used to being around and in the water. also butterfly is good for your body but is hard to keep going.

p.s please give me a good rating!!

I would say all swimming styles are good but I'd opt for stroke or for back stroke. The most important thing is to work with a plan and to measure time or pulse, because otherwise I find that you can really swim in laisure without improving your fittness. Please note that I am by no account a proffessional in this field.