I had a treadmill for fifteen years and just got rid of it about one year ago. I liked having it, but it was huge and I found it high maintenance in respect to keeping the belt centered.
I just bought an elliptical (which is still unassembled) but I decided on it because I thought it would be a better total body workout and take up less space.
I know a lot of women like the ellipticals better. I personally like a treadmill better. It just feels more natural to me. I would suggest visiting a gym (if your not a member). Usually they let you visit for a day for 5 bucks to see if you want to be a member. Then when you are there hop on the treadmill and the elliptical to see which one you want
I personally prefer an elliptical because I can walk and run outside and get soooo bored on a treadmill. However, from what I've heard and read a *good* elliptical is an expensive one. There are lots of cheaper ones out there, but they break easily or are too clunky to get an effective workout.
So for me, it's a gym membership until I am rich and can have a home gym
ETA: and of course, you should invest in whichever one you will USE most often.
I much prefer working out on an elliptical but part of that is because I *can't* run (things bounce too much and it's painful) ... and that means I can't get an effective high intensity workout on a treadmill.
I honestly don't think one is inherently better than the other. I think it's mostly personal taste and the one you'll use more than the other that's important.
I like the ellipticals better but I have both I got a cheap elliptical from walmart and I've had no problem with it at all in the 5 months that I have had it.
If you aren't sure I also suggest trying out a gym for a day or even go to a large sporting goods store, they usually have their demos on the floor and hooked up so you can try them out.
I have both and at this time prefer the elliptical (I like working the upper body too). However, just a suggestion -- I bought both of mine second hand. Exercise equipment seems to be something that doesn't wear out, just people stop using. The ellipitical is a $500 machine I bought for $50 from someone moving. (Check craigslist . com in your area )
I belong to a gym, so I have a wide variety of exercise equipment at my disposal. I use two different kinds of elliptical (one with stationary arms and an incline setting and one with moving arms but no incline), TM, stepmill, rowing machine, and spinners. I think they all provide a great workout. My preference is the TM, because I enjoy running and I can't run outside (knee problems). I run intervals on the TM so there's no question of being bored. Dying, maybe, but I'm not bored, that's for sure.
One of the primary advantages to the TM and one reason I like it is that it is easier to challenge myself on it. The TM sets the pace and I just have to keep up (or go flying off). Because of this, I've really been able to increase my running speed using the TM. I also get very consistent, high intensity workouts on the TM.
With the elliptical, on the other hand, I have to push myself. It goes as slow or as fast at I move. If I stop moving, it stops moving. I have to constantly be watching my RPM or MPH to make sure I'm keeping my pace up, otherwise, I start slowing down and I'm not getting the workout intensity I want.
So I agree with everyone else. Either one can give you a great workout, if you challenge yourself; it's just a matter of personal preference.