TradingView and Thinkorswim have very different candlestick charts. Which one is correct?

The charts here are cropped so aggressively that they're difficult to compare systematically. It would be better to include the price axis labels. I think the grid is $1.00 for TradingView and $0.50 for Thinkorswim. In addition, the time axis labels should be clarified. I think the first TradingView candle outside the yellow-shaded (premarket) area is 9:30-10:00 ET; I think the Thinkorswim chart is labeled in CT so the corresponding candle is the "8:30" red one.

Given these interpretations, I find the TradingView chart more consistent with other sources, including what I see myself in Thinkorswim. The Thinkorswim chart shown here, which I am unable to replicate, shows a clear sign of inconsistency: The open of each candle is often far from the close of the previous (for TradingView, as you can see, they are quite close). They don't have to be identical, but should be within pennies if no break in trading occurred between the candles (obviously, this is for intraday and doesn't apply between one day and the next).

Compare the raw numbers to see where the discrepancy lies. For example, are they using exactly the same time period for their calculation?. Do their 30 minute candles begin and end at exactly the same time and contain exactly the same price points?

If you have access to Time & Sales, cut and paste the actual trades and determine the O/H/L/C for the time period. Then compare that with the two sources and see which, if any, candle calculation is correct.

If you need that level of granularity for your trades then you should believe the tape, which is a record of all individual trades that occurred.

A candlestick is just a data point that contains 4 orders within a time period.

It is clear to me that they both recorded the same sequence of data and one just closed out their closing tick on different trade. When close is less than open, it will show the color for that. No big deal.