I chose Aurumoth, simply because in OU I feel it would have done the best. I enjoyed playing with it in CAP, even if Krilo and Necturna were more usable at times. Plus, Gen 5 CAP is where I started to take notice.
I picked Mollux because I love how well he performs against rain, and the shiny sprite is awesome! What I really hate though is how many of the gen4 CAPs have gone out of fashion, they don't really work anymore. Krilowatt for example is amazing in theory but when it has to deal with mollux and latias and Rotom-W you can see where it got less amazing. Voodoom is honestly horrible, weakness to fighting and no notable stats make it really poor. Fidgit and Stratagem are lost in a metagame full of rain and scald, fidgit can still work I guess but it isn't what it was. Arghonaut seems pretty bad to me, but bulk up still works maybe? It has good bulk, recover, and everything else it should need. Anyways this isn't the point of this thread.
I really like Mollux, Cyclohm, Revenankh, and Colossil. They are all so cool! I never liked tomohawk and necturna much because they don't look very natural to me.
I wnt kits, because hes a very good lead with good synergy with other CAP pokemans. He checks alot of things that other CAP's cannot dream of checking and it's fun to experiment sets with him. Almost anything i try ends up making my opponents want to kill themselves and it's very fun! :D
All of them are awesome, but in the end I ended up going with Cyclohm, Krillowatt, and Aurumoth. Those three have the designs that appeal to me the most, plus they fit my ideal playstyle of "take damage and dish it out too", which I don't think many of the others have.
Fidgit, because Poison/Ground + Vital Spirit and 105 Speed is just badass. At one point, I started using it on every CaP team back in the day. Didn't even run any attacks, just entry hazards, Rapid Spin, and Whirlwind.
Second (and first by design) would be Stratagem, because he's a motherfucker. Cool design and concept. Pre-Platinum, the thing was nearly unstoppable with Blissey out of the equation.
My favorite CAP would definitely have to be Tomohawk. As a fairly mediocre player and teambuilder myself, I've always found myself going back to balanced and bulky offense teams for the balance of defensive and offensive characteristics (since I hardly specialize in either). As such, I've always been partial to Pokemon that can take a hit and dish them out as well, which is why I have been very fond of Pokemon like Landorus-T. Tomohawk essentially sums up all of my competitive preferences in a way almost nothing else does. Fighting and Flying are my two favorite offensive types to abuse, and I've always been fond of a potential Pokemon with those STABs, which Tomohawk is. It even has the moves to abuse it; very little likes taking the combination of Aura Sphere and Hurricane, especially when backed by a very nice base 115 SpA stat. Tomohawk is also no slacker in taking hits with its great 105 / 90 / 80 bulk, Roost, good resistances with a Ground immunity, and Intimidate. It can even utilize Prankster SubRoost and Toxic to a great effect for a defensive stall set. Tomohawk also fills several great support roles with moves like Rapid Spin, Baton Pass, and even Healing Wish. Tomohawk just has the potential to fill so many great roles, and it makes a great symbol of bulky offense to me.
Necturna is definitely my second favorite. I have to agree with Birkal here, I was a bit worried as to just how a Pokemon with a one-time Sketch would work in OU. Since we were giving Necturna access to any one move it wanted alongside its natural movepool, we were walking very thin ice as to just how good we could make it. After all, we wanted a Pokemon that could actually abuse Sketched moves, but we didn't want to make it so good that it would break the metagame with the appropriate move. As far as the concept goes, I think Necturna was a slam dunk. She's just good enough to abuse Sketch in a fantastic way with several viable sets, and yet we were able to balance her typing, stats, and natural movepool in such a way to prevent her from being broken. She definitely deserves a mention.
Also, I'm not a huge fan of Aurumoth. Maybe it's just the direction that the project went, but I just feel that we gave Aurumoth a combination of stats, abilities, and a bloated movepool that just made it too good to be true.
I chose Scyclant because, although its hard for some people, I can use it to my advantage easily. I guess Scyclant really just depends on who uses it. However, when I first saw it I didn't know about the CAP project so I went a little crazy XD
It was a tough decision, since I liked so many of the CAP creations. However, I went with Mollux because of its defensive utility. It has two types of hazards, spins, has access to burn, poison, and paralysis, Trick, and reliable Recovery. Its stats are also good for what it does, and it is one of only two fire types that can flourish on rain teams (the other being Volcarona).