It all depends on what you're trying to do with it.
Nugget hunting for small shallow nuggets? - GMT
Nugget Hunting larger, deeper nuggets - TDI
Iron & nail infested sites - IDX Pro, IDX, Classic III
Wet saltwater beach sand - SUrfmaster PI Dual Field
Fresh Water - Beach Hunter ID
General All purpose coin, relic, & jewelry detector - V3i
Combination Relic, nugget shooting, and coin detector - MXT Pro, MXT
Easy Turn on and go coin & jewelry detector - M6
and on and on