For me, you can't do any better than him. That's not to say pieces by other artists can't have their own value, but if you're looking for authenticity to the source, you can' beat him, he not only gets the general details, but he understands poses that sum up Godzilla for each film so well, there aren't many pieces from him I don't admire and long to own. I will say, the '89 he did that Kotobukiya released as a 3 foot tall kit, is not my most favorite pose choice, it's like a mid-Biollante fight pose and without a Biollante attacking him, it's just not the coolest pose.
You can look at the shot of the '89 and '91 together and honestly, I don't see it as a difference of Sakai doing better with one or the other but rather, each being the perfect representation of their movie. Other than when fighting Biollante, that '89 is pretty much how he always looks through that movie, pretty basic poses. In '91 he gets more active and can be found in more action style poses and that's perfect embodied in the piece.