Static Generic Class as Dictionary

A static field in a generic class will have a separate value for each combination of generic parameters. It can therefore be used as a Dictionary<Type, whatever>

Is this better or worse than a static Dictionary<Type, whatever>?

In other words, which of these implementations is more efficient?

public static class MethodGen<TParam> {
    public static readonly Action<TParam> Method = CreateMethod();
    static Action<TParam> CreateMethod() { /*...*/ }
}

Or,

public static class MethodGen {
    static readonly Dictionary<Type, Delegate> methods 
              = new Dictionary<Type, Delegate>();

    public static Action<T> GetMethod<T>() {
        //In production code, this would ReaderWriterLock

        Delegate method;
        if(!methods.TryGetValue(typeof(T), out method)
            methods.Add(typeof(t), method = CreateMethod<T>());
        return method;
    }

    static Action<T> CreateMethod<T>() { /*...*/ }
}

In particular, how does the CLR lookup the static fields by generic type parameter?