1) Team Synergy and Structure :
Before voting, I'll like to ask everyone to consider the future picks of Team 1 and Team 2. As it stands, Team 1 has a Gengar while Team 2 have Dragalge and Victini. Since the Dragalge is a Toxic Spiker and Victini gets worn down fast by Stealth Rock, we know that Team 2 is going to need a Rapid Spin user (not Defog because it will blow away the Toxic Spikes Dragalge lays down). The RS users in OU are Excadrill, Starmie, Tentacruel, Mega Blastoise, Forretress and Donphan.
Picking Excadrill or Tentacruel will cause half of Team 2 to be weak to Ground moves so it is a no-go. Forretress and Donphan have their own issues which I won't bother discussing here. That leaves Starmie and Mega Blastoise.
Now, Starmie will want dual STABs (Water is for neutral coverage, Psyshock for a OHKO against Gengar) and one of Ice Beam, HP Fire and Thunderbolt. If we pick Dragonite or Garchomp now, Starmie will be forced to pick Ice Beam, leaving Team 2 open to Mega Gyarados and we can make Spinning difficult for Starmie by picking Ferrothorn who now takes nothing from it's attacks. Furthermore, Dragonite can simply pressure Starmie with the threat of a CB Extreme Speed.
Of course, Team 2 can simply go for Mega Blastoise instead but it wastes a Mega slot and is slow with no recovery so it is still a plus point for Team 1.
We also have to think carefully on what we pick because we have 5 slots left and we have several roles to fulfill such as Rocks setter, hazard remover, win-condition, wallbreaker , cleaner , utility, win-condition support, cleric, checks to a big threat, etc. . Of course, some are not needed but some of these roles are important and require one Pokemon each. Trust me, we do not want to be forced to pick Donphan, for example, to set up Rocks and Spin, just because we don't have enough slots.
2) Nominations:
CB Dragonite: My nomination. It has decent offensive synergy with Gengar who can punish Fairy-types with Sludge Wave while being able to take on Scizor and Bisharp. Dragonite also makes for a great early-game wallbreaker with it's high-power attacks and coverage while also being able to revenge kill threats late-game with Extreme Speed. This makes it easier for Gengar to clean-up late game. CB Dragonite, however, is a high-risk, high-reward Pokemon and is extremely reliant on prediction. It also needs hazards support since it is weak to Rocks.
Bulky Garchomp: I really like this one. Garchomp can set-up Stealth Rock for the team, pressuring Team 2 to pick a hazard removal or risk their teams being worn down fast. Furthermore, this will deter Victini from spamming U-Turn since it will take Rocks damage + Rough Skin each time it attacks. Having a Bisharp check and wearing down Talonflame (if it is picked) is also pretty sweet. Having only Rest as a method of recovery is a downside since it becomes set-up bait but it can be handled by a teammate.
Rhyperior: Does about the same things as Garchomp (Rocks setter that checks Victini and Dragalge) but has a weaker match-up against Bisharp for a better match-up against Talonflame. True, it can absorb the Final Gambit by Victini but personally (please don't take this as an offense), I don't think that's too much of a big deal since it will be crippled and left for death after that anyway. Has big issues with Special Attackers and crippling weaknesses to Water, Ice, Fighting, Steel and Grass. Oh, one more thing before I forgot, you are not allowed to have slashes in the set.
Unaware Quagsire: It is a good answer to physical set-up sweepers in general as Scizor, Bisharp, Mega Charizard-X, Mega Gyarados, etc. will struggle to get past it unless sufficiently weakened. Quagsire can take the physical priority attacks aimed at Gengar such as Scizor's Bullet Punch, Azumarill's Aqua Jet, Bisharp's Sucker Punch and Mega Pinsir's Quick Attack. However, Quagsire has very poor offensive presence and needs to be at high health to do it's job. It also doesn't fit an offensive team.