(Disclaimer: Items can be selected at your own decision, not everything works for everyone.)
Ability: Flame Body
Ghost typing gives good coverage for 2 E4 members, and fire type gives coverage to a swathe of other typings. Chandelure has a lot of resistances and two immunities, making it a good Pokemon to have on your team.
Virizion is your only normal counter, giving it a lot of importance for late game Plasma battles where normal types are fairly abundant. Depending on your item (i.e shell bell or leftovers), the last move can be changed out to your liking.
Ability: Compound Eyes
Galvantula is your main flying counter, and a secondary counter to water and grass. Compound eyes makes thunder more viable than thunderbolt, and volt switch allows you more room to swap your team around at will. Agility is good for creating a fast switcher, or slash is good for neutral coverage.
Your only electric counter, and your get out of caves free card with dig. Krookodile will also be your either primary or secondary Pokemon for the psychic E4.
Swoobat @ (I like to run scope lens from the early game, as woobat and swoobat learn a fair few flying moves with high critical ratios)
The flyer on your team and your main counter for fighting types and the fighting E4.
Samurott @ Mystic Water
Your surfer, Samurott is your main fire, rock and ground-type counter.
The only 'problem' with this team is that there is no dragon-type counter. To get past the Opelucid gym, it is helpful to substitute in a Beartic or Vanilluxe for your weakest Pokemon at the time. The preevolutions and occasionally the evolved Pokemon can be found before you reach Opelucid city.
If you pick either of the other two starters, I would recommend Carracosta as a good water-type replacement. Hope this helps someone!