Depends on your style. GSP has the perfect build for what he does and that is: 1. Using strikes to set up takedowns 2. Using wrestling to control your opponent 3. GnP the **** out of him Anderson Silva/Aldo have the perfect build for what they do: 2. Strike to kill 2. Use BJJ to avoid damage, subs and to catch opponents in subs IF they're taken down BJ also uses this same strategy, but he doesn't have the perfect build for it GSP has more muscle, bigger legs and is slightly tighter but p4p more explosive and powerful with his shots. Anderson/Aldo have longer, looser muscles, carry less muscle also, allows them to float on their feet and strike quicker.
At the moment it is the taller, longer, more athletic fighters who are controlling. Look at BJ, GSP, Silva and Machida.
I always picture BJ as short, but when I look it up and see him live he is actually pretty rangy for a LW at 5'9". I think it's a combination of seeing him against bigger fighters at higher weights, which also makes him look shorter because he is a little softer and rounder. I pretty much agree with the consensus though; there is no perfect build for a fighter because their is no perfect style of fighting. I think all things being equal in terms of being able to make weight comfortably, speed, flexibility, etc, that it is an advantage to be as big as possible. How you that size would be ideally spread out would vary on what you want to gain, because there are inevitably going to be trade offs. Beyond the fairly obvious advantage of strikers being taller with longer limbs or grapplers being thicker and more powerful, different body types lead to different styles within those pretty large boundries; traits normally associated with one can be surprisingly used as an advantage in the other. In grappling guys with long limbs like Aoki, Overeem, and Anderson, etc can use them essentially as longer levers to gain leverage that makes them deceptively good in areas they might be underestimated: Aoki's great Judo is helped because he uses his build so well and Overeem can damn near rip peoples head's off with his guillotine because he is so tall and his long arms make a great clamp around the neck. Also the triangle/armbar/omoplata attacks from guard can be made easier with long legs. With striking having a longer reach would always be ideal, but given that you only have a certain amount of bodyweight to work with, using some of it towards thickness and power can obvously pay off. Thiago Alves and Melvin Manhoef for example would to move up in weight if they were any taller or longer limbed, which would decrease their power advantage to at least some degree, although Manhoef's obviously travels to HW just fine. With striking it isn't just a matter of long limbed vs short limbed though; where Thiago Alves has relatively shorter arms and longer legs, so he has deadly leg kicks, BJ has relatively longer arms and a great jab.
I think BJ fighting bigger guys, being fat and having a big head gave us the wrong impression. I too thought he was smaller but at 155 and in shape you can see he is a relatively tall and long guy. I don't think there is a perfect build but I lean towards the rangey athletic guys. They've got the height and reach to strike and the dexterity and length to grapple well. Throw in the athleticism and it's what gives them the edge. Take the athleticism away and their build isn't worth much. However if I am going to put athleticism to a certain build then it would be the SLIGHTLY taller, more rangey guys like BJ, GSP, Silva and Machida. There isn't a perfect build but P4P we can't discount that BJ, GSP and Silva happen to be the best ever. At heavyweight, it's so open field with the weight that it depends on a **** load of things.
if you think there could be a perfect build i feel sorry for you... it is not about 'build'...there is a unique mentality that sets certain fighters apart from the rest... i mean look at cheick kongo, that feckers straight out of a greek coloseum! fights like it too! build means ****,i mean look at the podgy asassins bj and fedor or athletic freaks like gsp or carlos newton or rangy fighters like anderson etc thats the beauty of mma its the great equalizer...size,colour,physique it doesnt matter...if you've got it you've got it.