There's a lot of difference between a $200 metal detector and a $600 one. If the question is which is "best", the question should be rephrased to something like "less than $600".
One wonders what the purpose of the question was in the first place, it's like asking what's the best 4-wheeled vehicle in the $10K to $30K range-- a question so useless that not only does it have no answer, it can hardly even be the beginning point of a discussion.
If you're interested in buying a metal detector, as Ace suggested you need to offer more specifics.
Also since you're a newbie, I'll offer another suggestion: referring to yourself as a grave robber isn't likely to win you any popularity contests around here. Different alias might get better responses.
--Dave J.