Valvoline Advance, M1, Castrol Edge, and Pennzoil Platinum, and even Quaker State UD and the Warren Synthetics (SuperTech/AmazonBasics/Kirkland Signature) are all within a few inches of each other when it comes to performance. The difference is your application and what specs it must meet, the biggest being Dexos1 Gen2 (which is widely considered a all around solid standard when it comes to testing.)
Castrol EP/Pennzoil Ultra Platinum/M1 EP are a performance tier above the class listed above. They are able to handle a bit more abuse and typically have more detergent to keep the engine “just a little more cleaner than the rest.”
Castrol’s reputation as of late IMHO has been “meh.” Compared to the others, their product isn’t a standout at the price points they are offered at. Mobil 1 and Pennzoil are (for better or for worse) constantly coming up with newer formulas and seem to be on the up and up when it comes to meeting new specs. (Mobil 1 being better than Pennzoil, looking at you PUP...)
Bottom line - what and how you drive is a major factor in offering advice. Out of the two you listed, I would lean towards M1 EP.