Well let's compare:
Pokemon: Scolipede

Type: Bug/Poison
Ability:
* Poison Point: If user is hit my a Physical move, there is a 30% chance the attacking opponent will become Poisoned.
* Swarm:
- In Battle: If user has 1/3 or less of its max HP, Bug-type moves power increase by 1.5x.
- Outside Battle: If leading the party, Wild Pokemon encounters increase.
* (Hidden Ability) Quick Feet:
- In Battle: If user is inflicted by a status ailment, Speed increases by 50%. Speed decrease from Paralysis does not happen.
- Outside Battle: If leading the party, Wild Pokemon encounters decrease.
Weakness (2x): Flying, Rock, Fire, & Psychic
Resistance (.5x): Poison & Bug
Resistance (.25x): Fighting & Grass
Stats:
* HP: 60
* Attack: 90
* Defense: 89
* Special Attack: 55
* Special Defense: 69
* Speed: 112
* Total: 475
Learnset:
* Leveling Up:
Rock-type Rollout rolls over Flying- and Fire-types (especially if you had done Defense Curl the turn before) & Dark-type Pursuit chases away Psychic-types. In addition to that it learns Bug-type moves Megahorn, Bug Bite, and Steamroller which it gets STAB (making Megahorn extremely deadly and the other two still considerably powerful) and in addition to that it creeps out Psychic-types. Only worth wild Poison-type moves are Poison Tail and Venoshock and that's after you apply STAB. Other noteworthy moves would be Normal-type Rock Climb and Double Edge & Status moves Protect, Toxic, Agility, and Baton Pass.
* TM/HM:
Grass-type SolarBeam shines away Rock-types (remember if you use Sunny Day you won't have to wait a turn for SolarBeam to charge); Ground-type Earthquake, Dig, & Bulldoze bury Rock- and Fire-types; Rock-type Rock Tomb and Rock Slide entraps Flying- and Fire-types; Dark-type Payback punishes Psychic-types; Steel-type Gyro Ball spins around Rock-types; & Fighting-type Rock Smash breaks apart Rock-types. Other noteworthy moves are Bug-type X-Scissor (STAB plus Psychic weakness); Poison-type Sludge Bomb and Poison Jab (STAB), Normal-type Hyper Beam, Frustration, Return, Facade, Round, Giga Impact, and Strength; Type-dependent Hidden Power (suggested types would be Rock, Ground, and Water); & Status moves Double Team, Rest, Attract, Swords Dance, Swagger, and Substitute.
* Breeding:
Not much, there's Bug-type Twineedle (STAB plus Psychic weakness); Normal-type Take Down; & Status moves Spikes and Toxic Spikes.
* Prior Evolution:
It can learn Status move Iron Defense when it's a Whirlipede.
Pokemon: Galvantula

Type: Bug/Electric
Ability:
* Compoundeyes:
- In Battle: Raises Accuracy by 30%.
- Outside Battle: If leading the party, chances of encountering a Pokemon holding an item increases by 50%.
* Unnerve: Opponent is unable to eat any held Berries.
* (Hidden Ability) Swarm:
- In Battle: If user has 1/3 or less of its max HP, Bug-type moves power increase by 1.5x.
- Outside Battle: If user is leading the party, Wild Pokemon encounters increase.
Weakness (2x):Rock & Fire
Resistance (.5x): Fighting, Steel, Grass, & Electric
Stats:
* HP: 70
* Attack: 77
* Defense: 60
* Special Attack: 97
* Special Defense: 60
* Speed: 108
* Total: 472
Learnset:
* Leveling Up:
Nothing to battle weaknesses here. There is Bug-type Fury Cutter, Bug Bite, Signal Beam, and Bug Buzz (STAB); Electric-type Electroweb, Electro Ball, and Discharge (STAB); Normal-type Slash; Dark-type Sucker Punch; and Status moves Spider Web, Thunder Wave, Gastro Acid, and Agility.
* TM/HM:
Grass-type Energy Ball pulverizes Rock-types... and that's all Galvantula has to protect itself from it's weaknesses (sort of). We also have Bug-type X-Scissor (STAB); Electric-type Thunderbolt, Thunder (plus Rain Dance), Charge Beam, Volt Switch, and Wild Charge (STAB); Normal-type Hyper Beam, Frustration, Return, Facade, Round, and Giga Impact; Poison-type Poison Jab; Type-dependent Hidden Power (suggested types would be Rock or Ground); and Status moves Toxic, Light Screen, Protect, Double Team, Rest, Attract, Flash, Swagger, and Substitute.
* Breeding:
Not much, there's Poison-type Cross Poison; Dark-type Faint Attack; Normal-type Rock Climb; and Status move Disable.
FINAL CHOICE:
Scolipede

Though it doesn't have a unique type combination, from the moves it has the stats given it's the better choice of the two bugs. Scolipede is faster and defensive stats are better then Galvantula and its Attack stat is almost equal to Galvantuala's Special Attack stat. Either of Scolipede's Abilities will serve you well or at least better then Galvantula (except fr Hidden Ability). You can still choose Galvantula if you want a Bug- and Electric-type on your team wrapped up into one Pokemon, but a better Electric-type choice would either by Zebstrika or Eelektross.