best cardio exercise?

[Solarium]

I'll even add this.

Pick several of these that you like. I get bored with one very easily.

Jumping rope is brutally tough in my book. That's why it's effective.

Cross training will limit over use injuries.

My current cardio workout is something like this depending on time.

One day HIIT cardio on treadmill, slow speed 6 mph, fast speed 8.7 mph or so (adjust to your needs). The treadmill I use allows for a one button switch between the two. I do a 5 minute warmup, then at minute 5 go to fast speed, go back to 6 mp for two minutes and drop in the fast speed for minutes 8, 11, 14 and 17-20 (note the slow speed is for recovery in between). Believe it or not this will get you sweating.

One other day I do swimming. I'm a horrible swimmer so it's a terrific workout for me since I'm so inefficient at it. If I'm in the pool for an hour all my flailing has burnt alot of calories and I'm tired.

One day I'll do a long run on the road. Long meaning anywhere from 30 minutes to as much as an hour depending on how I feel. Either that or I've entered a race which may be anywhere from a 5-K up to a half marathon. Since it's a race I push it hard.

Recently I got a bike, so one day I'll use that. The weather is awesome and a bike trail or a race is great.

I lift 3 times a week.

I'm trying to change my cardio to one of more intensity but in intervals. I've posted my program on page 1, but thinking of doing what you're doing. Since I'll have a tough time switching between speeds, would doing 9.0 for 3 min, then 6.0 for 5 do as well?

I'm still having some trouble understanding the concept of the high-intensity-low-interval work out. Is the point of it trying to lose weight, train your cardio, or build muscles? Understanding this will allow me to adjust my cardio time and speeds. This interval high intensity work out really favors things that you can adjust on the fly, like an elliptical, especially with one that you can adjust the height as well.