which fullmetal alchemist do i watch first?

You can start off with any of these, to be honest. Brotherhood is 64 episodes and the main story line of FMA.

If you start off with Simple People, Tales of the Master, or Blind Alchemist it'll give you some backstory and insight on Brotherhood, but don't reveal any spoilers.

Although Milos is the FMA Brotherhood movie, it isn't a continuation of the series, so you can watch it before the series as well.

If you want to watch the OVAs/movie before the series to get you into the series you can. Or after you're done you feel like you're craving move FMA then you can watch it after. either way it'll be the same experience.

Brotherhood. In my opinion, it was 100x better than the original. Anyway, the others are episodes from the OVA Brotherhood. So they really don't have anything to do with the plot of Brotherhood. They are just like side stories.

You don't have to wait to finish Brotherhood to watch them. Like I said, they are just side stories so they wouldn't really have any effect.

watch the first one then then brotherhood because brotherhood crushes the original one.

watch the original first and then brotherhood

You know that