I've had this floating around in a notebook I take to work, and decided to write it out here.
Vehitrons are transformers who have as a alternate form a basic non-military vehicles. The majority of Vehitrons are Autobots, though there are vehicles on the Decepticon side as well. They do not have built in weaponry, generally, and instead favor hand held rifles, pistols, and melee weapons. Vehitrons are also able to generally evade and outrun most other transformers on the ground.
Optimus Prime, the Stunticons, Bumblebee, etc
Combatitrons are transformers who have as a alternate form a military vehicle. This is a slightly looser definition than some, as a combatitron can be a flying vehicle, such as attack helicopters, and other sub-sonic aircraft.They have innate weaponry in both robot and vehicle form and the majority have since sided with the Decepticon faction, though there are a few Autobot tanks and the like. They would rather fight than run away.
The Combaticons, Warpath, some versions of Megatron (tank)
Builders and engineers, constructitrons have as their alternate form heavy machinery that is best fit for construction and heavy industrial use. They are unarmed in their vehicle forms, and in robot form are predominantly either melee or brawl type fighters, or they retreat under the protection of their armed kin. They are seldom interested in fighting, and rather side with whichever side is in control in an area, or are a neutral third party.
Scrapper, Mixmaster, Hook, etc
These enigmatic transformers have as their alternate form primitive life forms, crustaceans, insects, spiders, and the like. They have a resource and reproduction based mentality and for every grasshopper and beetle, there is a giant spider, or praying mantis. They are seen as a lower class of transformer, scavengers and thieves, and otherwise undesireables. They are good scouts and vie with the Constructitrons for resource gathering missions. They respect and fear strength, so most aligned insectitrons serve under Decepticon coercion.
The Insecticons, Black Arachnia
Like the insectitrons, animatrons favor animal and lifeform alternate forms. But they favor higher order animals such as reptiles and mammals. Animatrons are explorers and trailblazers as they are somewhat uncomfortable in technoformatted cities and planets and prefer the uncivilized reaches of the galaxy. They lean more toward the Autobot faction, but those transformers who favor heavily predatory alt forms can develop a more aggressive pro-decepticon mentality.
Grimlock and the Dinobots, the Predacons, the Maximals, Ravage, Lazerbeak
Not to be confused with the Decepticon of the same name, Megatrons are transformers who are to their kin what transformers are to humans. Megatrons transform into transformer sized vehicles, spacecraft, even cities. They are truly gargantuan, but are passive by nature, only roused to robot form by dire need or demand. Megatrons are rare.
Metroplex, Trypticon, Omega Supreme
Not every alt form is mobile, there are fixed objects, such as observation arrays, traction cannons, and other forms. These transformers are 'generally' of a more cerebral nature and a less action oriented mindset. They are also fairly uncommon. Inanimatrons often rely on their peers to move them in alt form, or to use them in their alt form when they turn into a weapon or accessory.
Perceptor, Megatron (pistol)
Aerotrons are explorers of space and the limits of transformer ability. They transform into aerospace craft and are able to usually function inside or outside of an atmosphere. Their key attribute is that they are fast and agile. This is physically as well as mentally. Decepticon Aerotrons are frequently called Seekers. They are also typically armed and have enjoyed a long advantage over their more civilian Autobot adversaries.
Starscream, Thundercracker, the Aerialbots, Blitzwing
Even robots get old, replacing damaged or worn out parts with less than optimal ones. The result is that after a long enough time you are left with a robot that looks like Frankenstein in robot form and a rat rod or junk mobile in alt form.This isn't so much a race/faction as it is a physical condition. With time, a Junkion can be repaired or reformatted back to their original form. Likewise, a transformer with limited access to transformer 'medical' facilities will eventually become a Junkion just from making their own replacement parts.
A transformer can fit into multiple categories at the same time. The most obvious is the Junkion template, any transformer, from a seeker to a megatron can become decrepid and made of sub standard parts. Less obvious are combinations such as Aerotron/Megatron, where the transformer in question turns into a transformer scaled space ship. Likewise would be Combatitron/Megatron fortress robot. A transformer who turned into say a gun would be both a combatitron and an inanimatron. The side they formally appear as is largely up to the transformer in question.
What about Triple Changers?
Triple Changers have spent a bit more time learning alt forms. I would say that any transformer could become a triple changer if they felt the urge to and decided to spend the time and effort to learn how. The original series had Octane and Blitzwing, while Megatron has changed in just about every incarnation of the show, and changes forms between every one of the Bay movies (cybertronian jet, cybertronian tank, fuel truck).
What About Combiner Teams?
Combiner Teams are an interesting question, perhaps they are a transitional form between standard transformers and megatrons? Once a team starts working together long enough they separate less and less until they merge and all that is left if the gestalt form, and a newborn megatron, or a combiner team is born when a megatron starts breaking down mentally and then it's mechanical body does the same?