Live view has certain advantages that increase image quality. In Canon (and as I understand upcoming Nikon)the camera starts the picture electronically without the mechanical movement of having the shutter open. This eliminates one of the causes of camera shake and improves the sharpness of images. It is particularly effective in macro and long telephoto photography. Using a second screen to focus is particularly nice when the camera is at ground level and at one of those angles where it is nearly impossible to see through the view finder.
I am primarily a macro shooter and have probably 10 conventional macro lenses from various manufacturers in all of the popular focal length. As prime lenses designed for a specialty market, most range from fine to excellent, even the much older design. I would not pay much attention to the lens test: while they may be valid for the lens performance at a distance, THEY ARE NEVER TESTED IN THEIR MACRO RANGE. In terms of usage, I prefer lenses in the 90-200mm range. They give you more working space between you and the subject, which helps with skittish subjects and lighting. The longer the lens, the greater the distance between you and the subject, but the greater the weight you will carry (and the more you will tend to pay).
I would not shy away from 3rd party macro lenses. As a Canon shooter, I cannot comment about recent Nikon macros. I have used older versions of the Tamron 90mm and the Sigma 105mm and they were fine lenses (newer version are probably even better). I presently use the Sigma 150mm and the Sigma 180mm (the new version is better than the older) and both are exceptional.
The choice between the two lenses depends upon what you intend to shoot. They are both excellent lenses; they just are used to accomplish different tasks. The 100mm macro has a maximum magnification of 1/1. It can also be used a a general purpose lens since it focuses on lesser magnifications out to infinity. The MPE 65 has a minimum magnification of 1/1 and a maximum magnification of 5/1. If your intended subjects are the size of a grain of rice, then the MPE 65 will do a better job. If your subject is 2 inches long, then the 100mm will do a better job. Most people would find the 100mm a more useful and versatile lens. I have both lenses and use them both regularly
If you are after small insects, flower stigmas, or the like, it is a great lens. The learning curve is a little steep, as the depth of field is miniscule as you extend to 5x. Also a flash with a modeling light is extremely helpful as you lose about 6 stops of light at 5x. Focusing is by changing the lens to subject distance, as opposed to using a focus ring. That said, if you need high magnification and the flexibility of changing magnification it is a very sharp lens.
If you are going to work consistently in the 3/1 magnification area, then I concur with the MPE-65. It is very sharp. Using extension to get magnification favors a a short focal length macro lens(preferably reversed). You will need bellows, or extension tubes (at least two sets) because you will need extension in the amount of 4x the actual focal length of the lens to reach 3x mag. Reversed enlarger lenses on bellows or adjustable tubes also work well. One thing about shooting at higher magnifications. Be careful about stopping down too much to extend the miniscule depth of field. Diffraction will soften the image.