Swim Vs. Bike Vs. Run???

I'd do a little of everything so you won't fall out of practice with any of them if a tri is your main sport or end goal. I'm doing that at the moment and it's helping me build strength from head to toe. You can continue to get a good cardio workout on an elliptical too give your knee a break. I never knew that till I really busted out a workout on one one day as if I were running a race (it's so easy for me to dilly dally on those). Yoga has been awesome for strengthening my core and getting a good stretch after the weekend long run and soccer game. 

Whatever you choose, good luck! I'm with you on losing some fluff. 

Do all 3!  You don't need a training plan to work out.  I know several folks who have never done a triathon and swim, bike, run, and weight lift just to stay in shape and maintain a healthy lifestyle.  Also, eat right.  Eat healthy foods, monitor portion size, and work-out.  I bet you knew this was the correct answer though.

However, if you're a crappy swimmer and you have a a few months to spare; take some lessons and learn.  Make yourself more efficient.

IMHO 

Eat right

Swim, bike and walk.

Repeat until you drop some weight and slowly mix in the run. SLOWLY

Live in the pool and start putting some effort into diet. Doesn't have to a be a lot of effort, just try.

I started swimming and switched to diet soda couple years back and dropped the first 20 pounds quick.

Really swim though. The water doesn't melt the weight off, you have to do the work.  (I say this because I've seen some of the same people in the pool all the time slowly doing laps but they have been doing it for years and don't look any different to me.  3 minute hundred meters good.  30 minute 100 meters, um?)

But ya know what, while I can argue that swimming is a great workout and easy on the body impact-wise, do whatever gets you off the couch!

It's a lot easier to cut 500 calories from your food than it is to burn 500 calories.

If your goal is weight loss first, triathlon training second (or even after), adding weight training to whatever you do is a good idea.

If you build up a decent-ish bike base (3ish hours a week for a couple months), a high-intensity Spinning(R) class will burn some serious calories. Just don't do any weird crap like high resistance/low RPM, pushups or Godknowswhatawfulstuff bad instructors come up with. If it's a movement you wouldn't do outdoors on a ride, don't do it indoor cycling.

If you aren't a proficient swimmer, start NOW and get help. It takes a long time to build good swim technique.

X2

I lost about 50 pounds through biking and exercise. I've since lost about 20 more primarily from running every day. The thing is, when I train seriously for tri I tend to not lose anything. The fuel needed for training seems to balance with the calories burned.

Run-walk intervals can help a lot for the knees.  Start with a short run and long walk intervals and you can slowly work to long run with short walks.  Do all three (s-b-r) at least once a week but see if you can do one of them 3x per week, or 2 of then 2x per week, that's 5 solid workouts to start with.  Also you're all ready cross-training for your first race (why wait!).  See how you can integrate more training into your lifestyle for additional workouts per week.  Making the lifestyle change is often the hardest part.

Not for me, I'm always hungry. I'd rather train more than eat less. Just watch the quality of foods you eat, it's a lot more work to overeat produce, vegetables, and chicken or fish.

As someone with no sporting background before I tried to be a triathlete I am going to tell you something a little different to the others. It's something I wish I had heard at the start. 

1. Jump into it, gradually yes, build up slowly, yes, But jump right in. 

2. Get a coach for swimming or classes, or a dvd, or something but find out how to do it right. 

3. Don't let your weight or lack of form be or become  an excuse.

4. prepare to spend cash

5. Jump right in.

6. Do it, don't procrastinate.

7. Go for it.

8. Don't hold back, jump right in.

9 Swim Bike Run

10. When you are tired, Swim Bike run some more.  

Thank you all very much for the wonderful advice.

Once again, BT comes through for me!