Hmm...
This is a good question because I honestly don't know which past Godzilla is my favorite among them. I have qualities in all of them that I like and don't like. For example, GMK. I LOVE the bejeezus out of the eyes, but I hate the hunchback look. G2000, I love the body proportions, but I don't like the purple coloration of the spikes or the fact that he's actually green (I love the shape of the spines though). Godzilla vs. Mothra (original), I loved the evil look, but I didn't like the bell shape of his body. It was a bit too human.
Things like that keep me from having a true favorite, but if I had to pick a single suit that I liked the best out of all of them, it has to be Desu-Goji. That glowing suit with the lava-like rashes or whatever they were just made my jaw drop when I saw it for the first time when I was a kid. Also, the tone of that film was perfect. Well balanced with suspense, impending dread, and ultimately the sense that no matter what happens, humanity is going to lose. All of that culminates in my love for that suit.
When it comes to Godzilla 2014, I have my likes and dislikes about the design, but the likes FAR outweigh the dislikes.
I love the face, but I think the neck (specifically the throat) could be just a little bit thinner. Just a little. Right now he looks like he's got a pin head, though that does harken back to the Heisei series given the head/body ratio. I don't like the look of the torso, as it appears a tiny bit boxy in the toys and a little bit chunky in the belly.
However, I pretty much love everything else about it.