I Eat Francium

Bulbasaur line:

I mainly imagine the Bulbasaur line being used as therapy/emotional regulation/versatile service Pokémon! Mostly because of the natural aroma the bulbs/flowers on their backs emit :D

Bulbasaur have to be raised from hatching due to the wide variety of personalities this specie can have. Venusaur are very competent and calm Pokémon that have a naturally soothing aura, however if they aren't properly trained they may still be too boisterous or brash to be in public or resist their naturally playful natures.

Additionally, their tendency to wander in search of sunlight can prove to be difficult during training, and rainy seasons can become dangerous due to the sweet scents they emit luring in wild Pokémon.

Along with their rather large size and heavy bodies, Venusaur (and the Bulbasaur line in general) can't be entirely recommended for service Pokémon use- especially for people that need calmer and easier Pokémon, or those with allergies- but it is also incredibly rewarding to have them by your side.

Charmander line:

The Charmander line are mainly used as guard Pokémon, though their hotheaded natures can be difficult to train properly. These fiery lizards are constantly looking for a fight, which makes them highly territorial and willing to patrol their territory with relentless conviction.

This is a double-edged sword. Poorly trained members of the Charmander line can be highly aggressive towards strangers, an issue most commonly seen in Charmeleon. Their competitive natures and reckless tendencies lead them to be highly stubborn, which makes properly training them to heel and recall a challenge even for experienced trainers.

Many intermediate trainers will actively refuse to take Charmeleon and Charizards due to their heavily unpredictable competitive drive, so it is highly suggested that if one is planning on utilizing these powerful Pokémon as guards to begin their training as Charmanders as soon as possible with expert trainers.

Squirtle line:

Squirtle and Wartortle are popular pets, especially amongst young children and the elderly. Their bubbly and goofy personalities make them wonderful family companions, and their water typing means that they can also help with various types of cleaning and other chores. Squirtle are also known to be a popular choice for swim trainers, as their friendly faces and high swim speed make new swimmers calmer and safer being in the water.

On the flipside, Blastoise are often used for labor jobs. Their powerful cannons and high precision mean that their water blasts can be used as high-pressurized water lasers, and are extremely useful in factories that can't risk using fire Pokémon for cutting metal/steel during production.

Additionally, many commercial cruises use Blastoise alongside a number of other Pokémon for maintenance and guarding. Blastoise can easily keep up with commercial cruise ships, and their power allows them to keep away potentially predatory or aggressive Pokémon like Gyarados or Sharpedo. Plus, their water cannons can blast off pesky little parasites from the sides of these vessels without causing damage to the ship.

Chikorita line:

The Chikorita line are very popular as service Pokémon for similar reasons as the Bulbasaur line. Their natural aromas are quite soothing and even nurturing/healing, which is both highly effective for patients with various mental illnesses, disabled people, and people with chronic pain.

It is noted that Bayleef are not used as often due to the tendency for their aromas to invigorate others into 'fighting' moods, however overall this Pokémon line is very reliable, loving, and incredibly friendly and competent.

Cyndaquil line:

Despite their timid and anxious natures, Cyndaquil are actually highly sought after as companion Pokémon for similarly natured children. This Pokémon can grow with its trainer wonderfully, and more often than not a Typhlosion who has been with a trainer since hatching will be a fiercely protective and loyal friend.

On the other hand, Quilava and Typhlosion are typically used for Pokémon battling. Their flame-proof fur and complete willingness and drive to battle make them formidable foes, and their brilliant flames are always a sight to behold.

It is important to note that you should ALWAYS buy Cyndaquil from reputable breeders, catch them in the wild, or adopt. Due to their popularity in multiple different fields backyard breeders and other nefarious sellers have begun breeding the poor Pokémon en-masse to turn profits, and these Cyndaquil may have severe issues that heavily impact their quality of life (patchy fur, sputtering flames, etc.).

Totodile line:

The Totodile line are also insanely popular amongst battlers for their ferocity and willingness to take a bite out of anything they see. However, new and intermediate trainers are discouraged from trying their hand at raising one of these beasts, as even as a Totodile their jaws can crush bones and cause severe injury to those around them.

Surprisingly enough, it is actually incredibly difficult to acquire a Totodile due to this violent nature. Feraligatr are very clingy with their partners, often being incredibly difficult to separate and becoming aggressive if successfully pulled apart from one another. Along with being highly protective over their brood, breeders have had a historically difficult time with this specie line.

Treecko line:

Often utilized as livestock guardians in forested areas. Not only is the Treecko line territorial and highly intelligent, but their camouflage and movement through forests is highly important for their jobs. Along with their calm temperaments and focused precision, overall they are near peerless in their duties.

Additionally, they can be used as general guardians for trainers and other people. Retired Sceptile are known for their charming competence, carrying themselves with a confidence that naturally wards away wild or aggressive Pokémon. Many teachers actually have Sceptile for this reason, as they are diligent wards for children and surprisingly doting.

Torchic line:

Torchic are common pets for children, as their cutesy appearances and extremely huggable bodies are incredibly endearing to them. In the same vein, they are also a popular pick amongst the elderly for their soothing warmth and cuddly personalities.

Torchic are also good service Pokémon for this reason! Their soft, downy feathers and huggable warmth make them very good for grounding people, and they're quite well-mannered.

Combusken and Blaziken are common sights among battlers. Their combat aptitude and fierce fighting spirit make them very difficult opponents, and many are world-renowned champions.

The Torchic line suffers the same breeding concerns as the Cyndaquil line, though. Always buy from reputable breeders, catch wild, or adopt!

Mudkip line:

The Mudkip line are fantastic service Pokémon. Their sensory fins are fine tuned, allowing them to sense their surroundings with perturbing accuracy, allowing them to lead their companion without fear. Their strong eyesight compliments this, allowing them to scope out paths- even in the dark!- long before they arrive.

The Mudkip line also have extraordinary strength, which makes them even more versatile and useful. They can help trainers moving items, holding items, getting in/out of bed or other similar situations, and overall are very lovely and competent.