Theravada is the most orthodox and conservative tradition, as it tries to stick as closely as possible to the original teachings of the historical person of Gautama Buddha. Also the Theravada monastic order tries to maintain the original monastic rules from the time of the historical Buddha, although the Buddha allowed his followers to change the minor rules. It doesn't officially recognize any other "vehicle" apart from itself. There was only one turning of the Dharma wheel, according to Theravada.
The Theravada monastic order has done a good job maintaining the Pali Canon and its commentaries for 2500 years. It's true that later Theravada writings introduced exaggerations, but in general, most of the body of writings including texts and commentaries are kept close to the original.
The teachings of the Pali Canon (especially the Sutta Pitaka and the Vinaya Pitaka), the primary text of the Theravada tradition and from Theravada's perspective, the original teachings of the historical Buddha, focuses on the four noble truths, the noble eightfold path, the three marks of existence and dependent origination. Its focus is empirical and soteriological, not ontological or metaphysical.
In terms of culture and practice, Theravada temples introduced new innovations in terms of rituals, idols, chants and practices possibly to cater to the lay masses in Theravada countries who are not knowledgeable of the teachings. These are entirely optional of course.
Mahayana includes Vajrayana. The Mahayana tradition positions itself as the "Greater Vehicle" that teaches the path to Buddhahood, instead of just Arahantship, and presents itself as the compassionate path calling for the liberation of all sentient beings, as opposed to the "Lesser Vehicle" which is only concerned with one's own liberation.
The Mahayana tradition also introduced the second and third turning of the Dharma wheel, introducing teachings that it presents as being more advanced to the teachings of the "Lesser Vehicle" (which is limited to the first turning of the Dharma wheel).
The second turning of the Dharma wheel introduces the Bodhisattva vow, bodhicitta and Madhyamika emptiness. The third turning of the Dharma wheel introduces Tathāgatagarbha (also known as Buddha nature), the basis-consciousness (ālaya-vijñāna), the doctrine of cognition-only (vijñapti-mātra) and the "three natures" (trisvabhāva). Metaphysics was introduced into Buddhism through these, that is not in Theravada (which is strictly soteriological and empirical).
There are many more new introductions by Mahayana like the concept of non-abiding Nirvana (continued worldly existence after death, after full enlightenment), new Bodhisattvas with supernatural abilities, like Avalokiteshvara (compared to Theravada's recognition of only Maitreya) and the trikāya doctrine which says that Buddhas have three bodies, the Dharmakāya (ultimate reality), the Saṃbhogakāya (divine incarnation of Buddha), and the Nirmāṇakāya (physical incarnation of Buddha).
On top of this, Vajrayana (including Tibetan Buddhism) added tantric practices. Tibetan Buddhism also introduced the concept of tulkus (reincarnations of past teachers who are emanations of Bodhisattvas), dharma protectors, trances and mediums etc. Culturally, Tibetan Buddhism added mandalas, torma, singing bowls etc.
Some Mahayana and Vajrayana schools, like Pure Land and Nichiren, also introduced practices like mantra chanting for being reborn into Buddha realms after death or to become enlightened and so on. On the other hand, some other schools like Zen and Ch'an are focused on meditation.
Of course, the Theravada tradition does not recognize these newer teachings and practices, and sees them as departing from the original teachings of the historical Buddha. On the other side, Mahayana (including Vajrayana) sees its teachings as being more advanced, but still grounded on Theravada's teachings of the first turning of the Dharma wheel.
Which vehicle is suited to you? I suppose you can study them all and it's up to you to choose how many times you want to turn the Dharma wheel in your practice.
To understand how the Buddhist sects evolved, please read the book "Sects & Sectarianism" by Ven. Bhikkhu Sujato.