It depends on how much you will be dehydrating. For occasional use of small amounts, most anyone will do. As calendula stated, the Nesco is good. For regular usage and larger amounts, the Excalibur 5 tray is great. If you plan on large amounts, as in an extended food storage program, the Excalibur 9 tray is fantastic and hard to beat.
Also consider the space you have. I love LOVE LOVEmy Excalibur 9 tray, but it's as big as a large microwave. When I'm not using it, I have to store it in the basement.