Hmmm... I personally found myself to be quite fond of the Master Sword's 4th phase. When I was playing through Skyward Sword, one of the things that continued to recur in my mind, was the thought of finally obtaining the Master Sword at some point. When I eventually got the Master Sword, (in it's 4th phase) A wave of nostagia hit me and I was so elated! MY GOAL WAS COMPLETE. ;D Now, of course I didn't know that there would be a final "true" form of the Master Sword at this point, so I was pretty satisfied with my current Master Sword Phase. The thinner guard in the 4th phase reminds me of the Master Sword in Twilight Princess, and I prefer the muted colors over the brighter colors that are used in the Master Sword's final form. Now, don't get me wrong, I loved the 5th phase too, but I just seem to have a preference for the 4th phase's colors~
One thing that I do care for in the Master Sword's 5th phase, is that it has the Triforce on the part of the blade nearest to the hilt (the fuller?). I love that the Triforce was placed on the Master Sword in all of the different designs that it has had throughout the years- ALttP, OoT, TP, WW, and now SS. I found it peculiar that the Triforce wasn't placed on the 4th phase of the Master Sword forging in SS...