I personally prefer to have adjustability with a stem, but that is of course only because I have a very "downhill" aerobar position. I can certainly see though how a integrated stem bar combo might work for many.
Cheers,
Herbert
Litespeed/QR

I haven't seen how that feature lowers the weight.

Tom did a weight test of the various Vision Tech configuratons compared to the standard Syntace bar, C2s and WCS stem. The separate components were the lightest.

Hed. They are the best in my opinion when you look at weight, tunability, adjustability and value.

Visiontech will be second with their carbon product and their aluminum product is strong, but heavier has no integrated brake lever and does use an integrated stem.

The best reason to go with integrated bars over seperate components may be appearance. In some instances a minor serodynamic advantage may be present, but it is probably pretty small.

The Hed's are light, comfortable, stiff, adjustable and work with any good quality front plate mount 26.0 stem. I like them.

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Tom Demerly
The Tri Shop.com

As a new player in the aerobar market, Aero Concepts is first debuting it's integrated bar the Genesis. I still am a firm believer in this design. It eliminates weight, the frontal area is cleaner with fewer if any stem bolts, and is preferred by more time trialist. We offer the Genesis in 85mm and 100mm stems and our pads and extensions are so adjustable, that it will fit most riders. The pad placement is very low to the bar and we include risers for those who need to adjust their positions.

That said, for 2006, we will have a new aerobar that requires the use of a stem for the other half who prefer a bit more adjustability.

Both are sound designs and the obvious trend is for more adjustability but the traditional riders will usually choose the 1 Piece. My first orders were all from Europe where the 1 piece bar is still the bar of choice. The U.S. market is finicky and tends to go with the trends, thus the new designs with a stem.

The reality is that no matter what design you choose, you need to make sure it works for you. FIT and comfort should always be your focal point.

I personally use the HED one piece aero bar with an ITM stem. Nice combo, awesome bars. My close seconds would be Profile and Vision.
Herbert
Litespeed/QR

From what i can see is it doesnt matter if it fit you. I just got a set of used vision bars. The only thing i could adjust was the pad height. I had to add a spacer to the pads due to the fact that my head tube angle pointed the bars sligthly up. That mad eit real uncomfortable. Once I put the spacer in works great. Very low and getting more comfortable by the ride. The one thing I suggest is if you are getting an aggressive position get ones with a flat base bar. I do a group ride and staying off the aerobars for that long gets painfull in my arms and shoulders.