Alright, so for a sneak peak at what I'm conducting, I'll show you what I've thought would be the top 10 best starters:
Weavile Ability to Pursuit is ALWAYS a plus, in case of a person starts with a Ghost / Psychic lead, they regret the day. Able to Dance or wield a Choice Band and get things moving, Weavile's Base 125 Speed will cause major headaches to the unprepared. Having the best STABs arguably, Weavile can be a monster, but hampered by Stealth Rock and x4 Weakness to Fighting. But he's starting, so the former and mostly the latter is negated.
Gyarados Only the bulky versions should start, as using any other type of Gyarados is too risky. While Intimidate can factor many sweepers that want to physically hurt you right off the bat, Gyarados can Taunt slow starters and set up his dance. Though he is easily countered by some things (Gyarados does not outspeed Base 115s), he should be noted as a huge threat, as after he has two Dragon Dances under his belt, not much is stopping this thing. Great with an Electric-absorber behind, like Jolteon, Lanturn, or Electivire.
Yanmega Able to use Hypnosis or Taunt to get a good Speed Boost, Yanmega can sweep teams, that is, if he gets the chance to. Yanmega is harmed by his typing, but it's noted to be a big threat thanks to his 95 Base Speed and 116 Base Special Attack. STAB Bug Buzz is a nice choice, and if he chooses Tinted Lens, much will be hurt. Be aware though that it's not impossible to get past Yanmega, but it can be hard in the beginning.
Bronzong Able to do many things with his good defenses and typing, Bronzong can set up Trick Room, put fools to sleep, set up Stealth Rock, use his low Speed to his advantage, par-ish Special Attacks, and finally able to Explode in people's faces. There's a ton of shit that Bronzong can do. Gyarados leads can Taunt you off, but Bronzong is a respectable Weavile counter and even Yanmega. Fast leads can be crippled, in other words.
Swampert Though usually an early Stealth Rock is a good plus, being able to PHaze is another. This is why Swampert can start well. His typing has some useful resists, mainly Rock. Swampert can wield both physical and special attacks. Though he can't exactly counter Yanmega leads, he can take on a Weavile lead with Roar and at least use Hidden Power: Electric on Gyarados. Keep in mind though that it's move slot syndrome that kills Swampert.
Hippowdon Another bulky lead, but this time with Sandstorm. Sandstorm screws up all Focus Sash leads, and walls a couple of Pokemon. His only real reason to start would be Sandstorm though, as he can't really counter many other leads (perhaps Aerodactyl and something that lacks his weaknesses / sleep-inducing moves). He can set up Stealth Rock or PHaze, which should be a mention.
Also, keep in mind that Abomasnow will be combined with Hippowdon section, but Abomasnow will have info later. The slot here was for weather. It's not best to start out with Tyranitar, as he's countered by quite a few starters.
Crobat Though many people's jaws will drop, there should be a reason why Crobat SHOULD be mentioned. First off, he carries the fastest Sleep-inducer move in the game (not even Darkrai beats this thing). Second, Crobat can counter things like Heracross and Breloom (not the former on the start, as fear of a Scarfer might off-put this, but it is a given). Crobat can also wield Taunt to shut down things like Gyarados easily. U-Turn is also another big plus, as there's little prediction you have to do with Crobat in play. Though he can wield a Choice Band and wield Nasty Plot, Crobat's biggest disadvantage would be the inability to get some moves together. Other than that, Crobat can be a beast of a starter.
Metagross Pulling off a sweep is easy with this guy, and I'd suggest that he probably uses the AgiliGross set with Shed Shell (You need to escape Magnezone easier, so this will help. Though Agility + EQ is a mention, I'm just thinking about giving you a free move, like Thunderpunch / Meteor Mash / [Filler (Explosion / Pursuit)]. Metagross has, again, good typing, good defenses, and is a flipping tank. The ability to use Agility is a good plus, actually.
Jolteon The reason Jolteon is mentioned and not any other Electric-type is due to the fact that Jolteon can escape Dugtrio. Being able to pass Substitute and Agility (let's not forget a possibility of Charge Beam), Jolteon is very versatile. Able to wield Choice Specs with Baton Pass is a decent plus, as he is able to escape Dugtrio as well (with prediction). Hidden Power is his main problem, it's either he's walled by Garchomp or Swampert. If both are on the team, expect a couple of problems.
Though Zapdos can be a good option here, the problem is is that he's still hammered by being weak to Weavile leads. This is also a debatable choice.
Ninjask There is only ONE REASON why I've put this here, and that is simply the Baton Pass. As annoying as fuck as this can be, Ninjask is used in 4/5 Baton Pass teams. His favorite passes include Octillery, Cradily, and anything else with Soundproof. Other good options include Tyranitar, Rampardos, Marowak, Bibarel, Numel (???), and much more. Swords Dance and Speed Boost accompany each other, and with Substitute / Protect, it helps pull off both easily. A Choice Band variant is also quite powerful, as he is able to outspeed things quickly.
This is the list that I've conducted. I've also considered things like Ambipom and such, but it's walled by Steel leads easily. It is also to note that I did not include Scarfers only because that Scarfers are to suprise, and these are just what you would see commonly (or should, anyways). FEAR leads are also the suprise value, but should also be noted to be starters, but there is that problem of Sandstorm / Hail, which is common in OU.
Now for some that SHOULDN'T start:
Any Ghost / Psychic-type The reason being is simple: Pursuit. This ruins ANY lead whatsoever, and it's not stopped. U-Turning isn't a solution, as slower Pursuiters still nab you. This may not sound like a good reason, but it's for assurance. Gengar still makes a decent lead, but keep in mind that it may not be the best in some situations.
Electric-Types By looking at the obvious starters, it almost looks like you WANT to start with an Electric-type. But of course, there are a couple of problems. First off, you don't know for sure if Electivire, Jolteon, or Lanturn are behind to sap off the electricity, especially if Electivire takes advantage of it. The second one would be that if they switch to Dugtrio, many are screwed, barring Jolteon possibly, Zapdos especially, and I guess Electrode (though Electrode is UU). Not saying that Dugtrio is going to lead, it's just that it could be a good switch against the rest.
Dragons Even as of note, a Life Orb Garchomp with +Atk Nature, max Atk, and 1 Swords Dance on his belt will NOT kill Cresselia with Outrage, and Garchomp gets threatened by Ice Beam from Cresselia. There's also the fact that a couple of leads pack an Ice attack, such as Gyarados, which also has Intimidate to boot. If you still plan to lead with a Dragon anyways, be very, VERY weary of a counter.
The sections will be more in-depth, but these are just summarized. You can comment on this if you want. I'm throwing it on the front page as well, just incase if a person does read the first post through.