Choosing a manual focus or auto-focus lens mostly comes down to personal preference. If you want to use your lens for more than just macro photography, autofocus will be more versatile. Autofocus is generally faster than manual focus, so it's also ideal for moving subjects.  That said, manual focus is frequently the focus mode of choice in macro photography. Focus precision is critical in macro photos since the amount of scene in focus within an image is already so narrow that any off focus will be very noticeable. Manual focus gives you more control and lets you really hone in on the area you want in focus. So, if you plan on using a macro lens strictly for macro photography, a manual focus lens may be the better choice.