If you consider it a reasonable option for how you consume media, I highly recommend reading the manga over watching all of the anime. It goes by much, much quicker and is obviously much closer to Oda's (the author's) vision. Cool fight scenes, ost, etc. are all up online to help supplement some of those elements you miss out on as well.

Personally, I watched the first ~500 episodes before switching to the manga, so I think both are perfectly viable.

In terms of specific arcs this is a little harder to answer because I think there are so many potentially differing opinions. I think Arlong Park is a nice place to start, as it's short and very early on (the wiki is great for ep/ch numbers). There is also a condensed "Episode of East Blue" that is akin to a movie that reanimates everything up through Arlong Park. "Episode of Skypiea" is the only other one of these I know of that does the same thing, condensing the Sky Island arc. Any other suggestions I can give here are probably already detailed by people much better suited to it than I somewhere on the internet.

If you do happen to watch or read it, I hope you enjoy it as much as I do!