Given the 2 options listed, I'd go with Pheer without a doubt. Personally, I think "compression" based tracking is better than "tension" based tracking, or other words, I'd rather have a spring pushing my tracking arm up, than pulling it. I might, however, go with Ameribrade for their contact wheels and other accessories, as I think they're reasonably priced and seem to be decently put together.
Now all that being said, as long as the grinder is put together well, I'd hesitate to say that one design will grind a knife better than the other. As long as it tracks straight and is u should built solidly, you should be able to make good knives on any of them.
That's not to say that a TW-90 or a Northridge won't be a better grinder then either listed above, but at the end of the day, they'll all grind knives.