I'd recommend watching them in release order, as that's how most people have experienced them. You'll have a better understanding of the commonly ascribed strengths and weaknesses of the respective films and trilogies if you watch them this way. It is also very common opinion that each trilogy is substantially worse than the previous one, so if you watch them this way then you have an off-ramp at the end of the first and second trilogies if/when you've decided you've had enough - you'll never have to sit through bad films to get to the good ones.

The Machete Order is an interesting idea but I'm a little hesitant to recommend it because so many of these fan edits are designed by people who are in so deep that they tend to skim/omit information that is actually relevant to first time viewers who have no idea what is happening. Star Wars fans, like all fans of these geek franchises, often have a hard time seeing things from the perspective of people who don't share their obsession. For that reason, I also strongly recommend against watching any of the TV series or filler/standalone films until you've finished at least the first two trilogies, because they are written for Star Wars fans to flesh out the events around the main films and are filled with tons of irrelevant references and fan service that are just going to confuse and/or bore you.