Alternativa 3, aprovechando la función de @79137913
:
Saludos.

Código (vb) [Seleccionar]
Private Function MaxInArr(a() As Long) As Long
Dim max As Long
max=a(0)
For x = 1 To UBound(a)
If a(x) >max Then Max = a(x)
Next
MaxInarr=max
End Function
Saludos.