I've downloaded each of the applications at different times, and gave each one a trial run for a couple days. I was very surprised to actually find that I preffered Tellme over OneSearch, by far.
I found Tellme to be much faster. Starting from when it picked up my GPS location, up until the information I had requested was available on screen. I also liked that Tellme had more search options and information available. I was stoked when Yahoo released OneSearch with voice command, and promptly downloaded it to give it a whirl. I found it simple and easy to use. A bit slow at times, worthwhile though since no others had software like it. However, Microsoft outdid Yahoo, by far with their release of a product that doesn't even match but far surpasses the previous. Just wanted to share my opinion on the two. I'm not saying I'm right or wrong, just my opinion. I would love to hear other people and their opinion on the two products. Thanks!!

Wirelessly posted (@ 72 mph)

I tried them both, and I have to admit that Yahoo!OneSearch with voice works better for me. The search speed is really fast, havent had any problems with it yet! Gets it on the mark everytime!

Just asked this question in the Yahoo oneSearch thread.

I prefer the yahoo oneSearch for the search results- especially if I'm looking for web results. However I prefer the tellme functionality for directions, maps etc.

I will keep them both.