The direction that someone takes in their Dharma practice actually bears little difference to the end result, but depending on their motivation to practice and also depending on how much effort they are willing to dedicate and put into their Dharma practice. Sometimes, it is not a real reason for them not choosing a certain path, but rather it is merely a cover for their own shortcomings with regards to Dharma practice. I have met many Theravardans who refuse to learn or explore Vajrayana or Mahayana for the reason that it is too complicated when they dont even take the time to learn or have gone through the basics and investigations first before making that statement. I have also met the ones who think that they are practicing the "pure" and "untainted" teachings of the Buddha by sticking to the "safe" teachings, teachings that the Buddha have actually taught based on scholarly discernment, or that is what they would like to believe. My question is, why use Buddhism to protect and strengthen our own ego? To study only the 'purest' even if it would not be of any benefit, but only to feel 'safe' is nothing short of self preservation which is but an extension of the ego and self cherishing. So...why practice the Dharma again?
With that said, there are people who genuinely prefer the theravarda tradition and they put a lot of effort into studying and practicing the teachings and they gain results from there. Those are genuine in their claims when they say that Theravarda is for them as the Theravarda's share of the tripitaka is quite vast as it contains all the Sutras (discourses), Abhidharma (philosophical commentaries on the Buddha's teachings) and Vinaya (the explanation of the monk and nun vows, rules and regulations as well as explanations related to the vows.) there are people who really study those and put those into practice as opposed to just saying they prefer theravarda and stopping there and only skirt around the basics instead of learning and practicing more. There are also Mahayana practitioners who discriminate against Theravarda, saying that they are lesser and inferior and dare not explore Vajrayana because they are afraid of learning "the wrong lineage" and they cannot turn back after that. Sometimes, its something we can observe in others but are powerless to stop.
For me, I choose Vajrayana because i know it encompasses both the Theravarda and Mahayana. I did my investigations of all 3 traditions, and I know what all of them are about in a nutshell, and I have decided that Vajrayana is the tradition i belong to as it answers most of my questions and feels more complete in a sense that the text does not look it was truncated or edited to remove certain elements that are deemed superstitious or due to lack of understanding from the editor.