I don't know which one is more accurate though. If chartex has faster and more accurate data, then it's their strong point (reason to use). But how to prove that?
Regarding accuracy, it's actually the same as in any tools. because the retrieved data is from Uniswap.org API. However, here the problem is the speed of the system in retrieving data from the parent. Therefore, every 3rd party such as ChartEX and other services will display different price or volume data. So, to find out the volume and price accuracy, of course the user can only get it from the parent, not from the 3rd party. But, the different data mostly it will not too far. (CMIIW)