Between those two options, I’d go with the original. Know full well that the pacing of the original show is a little all over the place, ranging from way too slow to stupidly fast on a whim. However, the writing is better than the new show (imo), the direction is awesome and ultimately the journey of the story is complete and concise. You’ll definitely feel like you want more by the end, which is how you want a show to be.

Stampede is new, but it suffers from some poor pacing decisions and bad writing. It takes the manga and condences the plot points majorly while adding some of their own. It’s not terrible, but I’d argue the characters feel a bit like paper standee versions of themselves due to how little development they’ve given the characters and how quickly they went through critical story beats.

So I’d watch the original and then read the manga. Once you read the manga, you’ll know what to expect from the characters and then the writing issues of stampede become a bit less of a problem (though still annoying imo)