The question people are really asking
Someone who has just learned that their Sun sign differs between the two systems usually wants to know which of the two labels is the real one. It is a fair reaction, and the honest answer is that the premise does not survive contact with how the systems are built. Both calculate the sky correctly. Given the same birth data, a tropical chart and a sidereal chart agree exactly on where every body was — the same ephemeris underlies both, and any disagreement there would be a software bug, not a school of thought. What differs is the coordinate origin each uses to name those positions. Two rulers reading the same length from different zero marks are not competing for accuracy.
They are measuring different things
The tropical zodiac is anchored to the March equinox, so it describes the Sun’s position within the cycle of the seasons. When it says Aries, it means the first twelfth after spring begins in the northern hemisphere. The sidereal zodiac is anchored to the fixed stars, so it describes position against the constellations. When it says Mesha, it means a specific stretch of the star background. Both statements can be true of the same instant, because they are about different reference frames. Asking which is more accurate is close to asking whether a temperature is more accurate in Celsius or Fahrenheit — the question that has an answer is which scale you meant to read.
Both are internally consistent
Each system has had centuries to build interpretation on top of its own zero point, and each is coherent within itself. Western astrology developed a body of meaning for tropical positions, a house system, a set of aspects and a timing method by transit and progression, all of which fit together. Vedic astrology did the same for sidereal positions, with whole sign houses, its own aspect scheme, the nakshatra layer and the dasha periods. Neither borrowed the other’s foundations, so neither can be evaluated using the other’s. Where problems appear is in the mixing: a sidereal chart read with tropical sign meanings, or a Vedic period system applied to a tropical placement, is not a fair test of either tradition.
What can and cannot be compared
Some things are straightforwardly checkable. Whether a chart correctly reports the sky, whether an eclipse date is right, whether the ayanamsa applied is the one advertised — these are arithmetic and can be verified. Whether the interpretations that follow are true of a person is a different sort of claim, and it is not one this page is going to settle in either direction. It is worth saying plainly that no scientific evidence supports astrology’s predictive claims in general, which is a statement about both systems equally and about neither in preference to the other. Accuracy in the astronomical sense is available to both; accuracy in the interpretive sense is not established for either.
How to choose in practice
Since the systems are not in competition on their own terms, the reasonable basis for choosing is fit rather than verdict. Vedic astrology offers finer granularity — nakshatras, divisional charts, a lifetime period sequence — and a more prescriptive, event-oriented style. Western astrology offers a psychological vocabulary, a rich literature on the outer planets, and a chart most English-language material assumes. Some people find one framework more useful for thinking with, and there is no reason not to explore both. What is worth avoiding is treating the difference as a discovery that your familiar chart was fake. Nothing about learning your rashi invalidates the Sun sign you have known for years.