Alien and Impinj work just fine, however I encourage people to stick with Motorola for the following reasons:
1. Typically less expensive
2. Well tested with proven performance and reliablity
3. The FX9500 offers an 8-port model
(the biggest reasons)
4. If anything happens to your Motorola reader there is a greater chance I can help you fix it since that is what I'm most familiar with. Currently I don't have an Impinj or Alien reader at my house. So it would be difficult to troubleshoot other brands.
5. I'm a Motorola "Partner", so if you purchased a reader through my company and I can't resolve the issue then I can pass the issue up to Motorola and they will work on it. If you purchase another brand then you'll have to deal with whomever you purchased through and hope they care about providing good support for their products.