To my mind the advantage of implicit localization over explicit localization is that if you have more than one property to localize for a given control, it's a more economical syntax.
In the case where you just need to localize some text I use the asp:Localize control which only has a single property (Text) that renders to the UI. Is there a reason to use one over the other? Any style preference? Are there any speed differences?
Implicit
<asp:Localize ID="Localize1" runat="server" meta:resourcekey="Something" />
vs
Explicit
<asp:Localize ID="Localize1" runat="server" Text="<%$ Resources:Something %>" />